Networks in more depth

Networks in more depth - Transcript

Communication and Information Technology
Section 15 Networks in more depth
Recommended reading
B Daley 2007 Computers Are Your Future Prentice Hall Chapters 2 3 8 9
B Daley 2006 Computers Are Your Future Prentice Hall Chapters 2 3 8 9
B Daley 2005 Computers Are Our Future Prentice Hall Chapters 6 7 8 9
B Pfaffenberger 2003 Computers In Your Future Prentice Hall Chapters parts from 7 8 9 10 11 12
B Pfaffenberger 2002 Computers In Your Future Prentice Hall Chapters 6 7
O Leary T J O Leary L I Computing Essentials Complete Edition 2001 2002 McGraw Hill Higher Education 2001 Parts from Chapters 7 8
Introduction
Approximately 50 of the UK population has access to the internet Most of this access falls into one of the following two categories
Narrowband typically 56k modems over the phone network
Broadband typically cable modems from Virgin Media formerly Telewest and NTL or ADSL using the BT network
Analogue vs Digital
An analogue signal can take any value between its minimum value and its maximum value Thus if its minimum and maximum values are 0 and 100 respectively then the following could be an analogue signal
34 37 25 98 47 03 17 96 11 14 67

A digital signal is can take only two values on one or off zero Thus the following could be a digital signal
1 1 0 1 0 1 1 0 0 0 1 1 1 1 0 1 1 0 0 1

Analogue Quality of Service
The most amazing thing about the internet especially for those who connect over a 56k modem is that it works at all let alone as well as it does The basic technology used for a 56k modem is over 100 years old
Despite this the internet permits the establishment of a direct computer to computer connection between any two computers on the internet And the internet generally works as a whole 24 7 365 though specific problems can cause problems for specific parts of the internet e g the customers of a particular ISP
Most of the telephone systems in developed countries are based around copper wiring The speeds at which computers can transfer data over such connections has always been limited the first analogue computer modems could transfer data at 300 bits s while a 56k modem can transfer data at about 57 600 bits s and although improvements have been made we are at the physical technical limit now
Complete failure of the internet is a very rare occurrence indeed One famous infamous instance was the release of the shareware try before you buy version of Quake when the phenomenal demand for the 20mb install file crashed most of the US telephone system The company that released Quake was told never to release software in a similar manner again e g they should release it on computer magazine cover disks first
Who runs owns pays for the internet
Nobody runs the internet The internet comprises millions of computers networked together Some networks such as that of the University of Dundee comprise thousands of individual computers There are however standards regulations to ensure that all of these millions of computers can communicate with each other safely and efficiently
There are several organisations that attempt to set these standards through agreement with interested parties They typically issue a Request For Comment RFC which elicits feedback Over a period of months years these may lead to agreement and new standards
One of the most important organisations is the Internet Society which like many of these organisations is a not for profit organisation there is a widely held belief that the standard setting procedure should not be hijacked for private gain
The World Wide Web Consortium W3C sets the standards for the www There is an ongoing issue of standards compliance i e non compliance amongst the main www browsers e g in the past both Internet Explorer and Netscape Navigator introduced technologies that are not ratified by the W3C or cannot handle all of the standards and as a result not all www sites can be viewed properly in all www browsers Each tries to use browser specific technologies to force internet users to adopt their browser In time the W3C is typically forced to accept these standards as de facto standards since so many people use these www browsers Other common browsers such as the increasingly popular Mozilla Firefox and the longer established Opera have a much better record when it comes to standards compliance
Recently some firms have tried to get some of these internet standards organisations to adopt their patented technologies as standards This would mean that you might have to pay to view pages using those standards This is strongly resisted by internet pressure groups such as the Electronic Frontier Foundation EFF who argue that no one should own the internet For example Microsoft has wanted to add new features to email to reduce spam but this would involve using its technologies which could give it the right to demand a fee for every email sent The EFF is very successful at raising funds to finance lawsuits in defence of internet freedoms
One of the most controversial issues at the moment is the ownership of www domain names The system as a whole is run by the Internet Corporation for Assigned Names and Numbers ICANN but the actual process of registering domain names e g amazon co uk www dundee ac uk is delegated to registrars who will register your domain name for a small fee The controversy stems from the fact that there can be more than one claim to a particular domain name especially common ones ending in com
Specifically people can attempt to extort money from organisations by registering domain names similar to the organisation s name and offering to sell the rights to the domain name at an extortionate price Such people are called cybersquatters
However another issue of concern is the control that the US government can exercise over the internet most of the main internet organisations are based in the USA and hence are subject to US national law There is evidence to suggest that where there is a dispute between a US firm person and a non US firm person the decisions tend to go in favour of the US firm person Furthermore the US government can use its control over the internet as a tool of foreign policy
Recently there was an attempt by the United Nations one of its agencies to give control over this and other aspects of the internet to the United Nations however the United States successfully resisted this move
Most of the costs of the internet are borne by private companies universities and private users However some of the internet backbone is funded by national governments especially the US government
Internet Service Providers
Some individuals gain access to the internet via their employer or through their university but many people rely on a private company to provide their internet access Such private companies are called Internet Service Providers ISPs For a small monthly fee they can access the internet by connecting their computer to the ISP s computers A minority of home internet users in the UK use a 56k modem to contact their ISP over an analogue phone line an increasing majority use broadband
TCP IP
The TCP IP protocols
The TCP IP protocols are fundamental building blocks for the internet TCP stands for Transmission Control Protocol while IP stands for Internet Protocol The TCP IP protocols manage how data is sent over a network whether it be a local area network LAN or the internet as a whole
When you send information over a network the TCP IP protocol splits that data up into smaller chunks called packets which include information required to get the data to the required computer When they arrive at their destination they are joined up together again Each packet is no more than about 1 500 bytes
The TCP protocol is in charge of the splitting and eventual joining up of the data while the IP protocol is in charge of the sending of the packets to the right destination
Winsock
TCP IP are protocols a set of standards rather than a program as such For Windows computers there is a program called Winsock that actually handles the job of complying with the requirements of the TCP IP protocols
Packet switching vs circuit switching
TCP IP uses packet switching whereby individual packets from the same item of data sent from a source computer to a destination computer can be sent via different routes There is never a consistent direct connection between the two computers
On the other hand a telephone call uses circuit switching whereby a direct connection is made between one telephone and the other and all of the data i e the audio is sent along the same part of the network that is temporarily set aside for the sole use of that telephone call
This difference between packet switching and circuit switching has important implications for what happens when the network is congested With packet switching the packets will get there in due course but they could be delayed whereas with circuit switching the call is either connected and is fine or is not connected at all
The network hardware
The connection
There are two ways to actually physically connect to the internet
connect to a network e g a LAN your computer must have a network interface card NIC and a cable connected to it connects you to the network this is the situation with computers on the University of Dundee network cable modems from Virgin Media and ADSL from BT and others
dial in to the ISP using an analogue 56k modem over the phone line
Hubs bridges gateways repeaters routers
hubs link groups of local computers together and permit communication between them
bridges link together different LANs permitting external communication to take place
gateways permit the transfer of data from one type of network to another
repeaters amplify data to ensure that the signal does not weaken despite the long distances the data might travel
routers decide the route that a data packet will travel to get from the source computer to the destination computer the data packet will be passed from one router to another each time getting closer to its destination when deciding the route a data packet will take routers take into account any bottlenecks in the internet so the route is not always as the crow flies furthermore packets may arrive out of order
The internet backbone vs the local loop
The internet is truly global and so a lot of data is being passed very long distances For most of this distance the data is being passed from one router to another router along the internet backbone high capacity high cost connections When the data gets to the individual home computer user it travels along the local loop which has a much more limited capacity
Most of the local loop in the UK was built by BT It has used this near monopoly to generate monopoly profits by keeping prices high Many other companies wanted to end BT s control of the local loop to offer unmetered internet access you pay a flat monthly fee rather than a per minute fee and eventually this became a reality

Latency dropped packets and error checking
Latency
Many computer users use the term the world wide wait to describe their surfing experience even if they have a broadband connection such as that offered by BT or Virgin Media The simple fact of the matter is that the connection speed to an internet site is determined by the slowest part of the route not the fastest part of the route
You can view the route between you and an internet site through the use of the DOS command tracert Yes from time to time you DO need to know how to use the CLI The output below was the tracert result for the connection between my office pc and the university web site home page
M tracert www dundee ac uk
Tracing route to duxweb dundee ac uk 134 36 2 84
over a maximum of 30 hops
1 10 ms 10 ms 10 ms 134 36 98 1
2 10 ms 10 ms 10 ms duxweb dundee ac uk 134 36 2 84
Trace complete
To ensure it does not report one off extreme results tracert actually does the trace three times In the above case the whole route was undertaken in less than 10 milliseconds i e very fast
Dropped packets
The close geographical proximity of the duxweb dundee ac uk server to my office pc and the fact that I don t leave the University of Dundee LAN ensures that the tracert produces excellent results However
M tracert d www microsoft com
Tracing route to www microsoft akadns net 207 46 230 220
over a maximum of 30 hops
1 10 ms 10 ms 10 ms 134 36 98 1
2 10 ms 10 ms 10 ms 134 36 168 1
3 20 ms 10 ms 10 ms 146 97 250 65
4 10 ms 10 ms 10 ms 146 97 37 25
5 10 ms 10 ms 10 ms 146 97 35 53
6 20 ms 10 ms 10 ms 146 97 33 22
7 10 ms 10 ms 10 ms 146 97 33 26
8 20 ms 20 ms 20 ms 146 97 33 30
9 10 ms 20 ms 20 ms 146 97 35 6
10 30 ms 20 ms 20 ms 128 86 1 249
11 20 ms 10 ms 20 ms 195 66 224 77
12 20 ms 10 ms 30 ms 212 113 0 114
13 21 ms 20 ms 30 ms 212 187 131 34
14 80 ms 90 ms 80 ms 212 187 128 153
15 170 ms 170 ms 160 ms 209 247 10 133
16 180 ms 180 ms 190 ms 64 159 16 99
17 170 ms 160 ms 170 ms 63 211 220 82
18 171 ms 160 ms 170 ms 207 46 190 117
19 171 ms 170 ms 170 ms 207 46 129 175
20 170 ms 170 ms 207 46 190 26
21 Request timed out
22 Request timed out
23 Request timed out
24 Request timed out
25 Request timed out
26 Request timed out
27 Request timed out
28 Request timed out
29 Request timed out
30 Request timed out
Trace complete
This tracert to www microsoft com at 4pm UK time 11am US EST time is a total disaster Basically the page took ages to download The slow connection is indicated by the fact that the times get longer the further along the route we go From router 20 onwards we start to get s instead of speeds this indicates dropped packets i e the packets simply never made it The fact that they have to be sent again ensures that the speed is slow with a capital S
Error checking
When TCP creates packets to send over the internet it includes in the packet a checksum a number that summarises the contents of the packet A numerical analysis is done on the packet and a number the checksum generated from that numerical analysis Once the destination computer receives the packet it checks to see if the contents of the packet match the checksum and if it does not match then the destination computer knows that somewhere along the route from the source computer to the destination computer the packet has become corrupted If so the corrupted version of the packet can be discarded and a new version of the packet requested
Domain Name Servers
Domain Name Servers
In the tracert results above we saw that www dundee ac uk is a server with the IP Internet Protocol address 134 36 2 84 This connection between the URL users would type in and the IP address that the internet knows it as is handled via the Domain Name System You type in the URL and you are sent to the underlying IP address This IP address is unique and hence addresses a unique internet site
This translation of the URL into the IP address is undertaken by a Domain Name Server DNS Any organisation providing internet access e g the University Virgin Media etc will have their own DNS If the organisation s DNS goes down then typing a URL into a www browser will not connect you to that www site if you know the IP address then you can type in that and get to the site but how many of us remember IP addesses
There is an organisation called InterNIC who has responsibility for maintaining the master copies of the connections between URLs and IP addresses from which individual DNSs can update their information They keep these vital pieces of information on nine at the latest count different geographically spread servers Take out these nine servers and its bye bye internet Even taking out only some of these nine servers can cause massive disruption to the internet
More on IP Addresses
IP addresses come in ranges some of you will have noticed the similarity between the IP address of my office machine and that of duxweb dundee ac uk
134 36 2 84 duxweb
134 36 98 1 my office pc
All University of Dundee computers should have an IP address starting 134 36 while all those in the Economic Studies department have an IP address beginning 134 36 98
There is also an important distinction to be made between a dynamic IP address you get a new IP address every time you log on and a static IP address you get the same IP address every time you log on If you connect to the internet over a dial up 56k connection you will get a dynamic IP address The university has a combination of dynamic and static IP addresses In some instances a static IP address is very much advantageous some internet applications require the knowledge of the IP address of a computer you are trying to contact and so with a dynamic IP address this information is frequently changing
Client server
Most of the data flowing across a computer network including the internet is flowing between two computers operating on a client server basis The server also known as the host contains the data and the client requests some of that data The client requests data and the server delivers that data to it The data that is sent may already reside on the server in the required form or may involve some processing querying first in order to create it
An example would be a www site The web site administrator will have set up standard web pages on their server e g the home page The web site user connects to that web server from their client downloading one or more of these standard pages When the user uses the search function in the web site the server processes that query and creates a new temporary web page containing the results of that query and sends that information to the client
It is not just the www that operates in this fashion it applies also to email ftp newsgroup servers etc
It is frequently the case that a server will serve information to lots of clients at the same time for example the BBC News www site might have tens of thousands of concurrent connections to clients and there are some servers e g www microsoft com that probably have a lot more than that This has implications for the scale power of computers while the clients may be and typically are small computers such as those for sale on the high street the servers need to be much more powerful and thus can cost anything from tens of thousands of pounds right up to several millions of pounds These large server machines are specifically built to deal with these demands and contain components not seen in the high street type computers
This is also an area where standards play an important part In particular it is not necessary for the client and the server to be using the same operating system and software so long as the operating system and software on both machines adheres to the same standards Thus while most www browser clients are either Mozilla Firefox or MS Internet Explorer the most commonly used www server software is actually called Apache And while most users browse the web on a Windows based computer more and more servers run on the alternative operating system Linux But so long as all adhere to the same standards they should all get along just fine
In the case of the www the relevant standard for transferring data between a www server and a www client is HTTP HyperText Transfer Protocol
Firewalls
The internet community is in many respects like society at large it contains good people and it contains bad people Part of being able to use the internet successfully is the ability to protect yourself from the harm that bad people try to do to your system and in particular the data on it and in this respect firewall software plays a very important part
There are actually many ways in which gaining access to a computer s resources can be damaging to the owners of that computer for example they could
delete the data e g wipe the network hard disks where all student work is stored
modify the data e g in the student performance database turn a mark of 35 into 75
steal the data e g steal credit card information from an online store or from your home computer
use the computer in an attack on another computer see Denial of Service attacks below
Firewalls control the flow of data between either a single computer and the rest of the network internet or between a group of computers and the rest of the network internet The idea is to permit those protected by the firewall to continue to access the network internet as normal but prevent others from gaining unauthorised access to the computer resources protected by the firewall
There are many different types of firewall ranging from cheap and cheerful personal firewalls that will adequately protect 99 9 of home users through to corporate firewalls designed to maintain the protection of large corporations with an internal network spanning the globe Personal firewalls are typically very cheap free or 20 or so software based and fairly easy to set up and maintain Corporate firewalls are often very expensive thousands of pounds based on both software and hardware and can be difficult hard work to maintain
One of the most common functions of firewalls is packet filtering the firewall examines the header of every packet to see what kind of connection is being undertaken and between which machines and can block the packets if it thinks it might be dangerous either the packet is suspicious or the sender receiver of the data is suspicious
Choke routers
Not all frowned upon internet connections are nasty illegal hacking it may simply be the case that an organisation does not want its resources used for a frivolous use or its staff wasting time So for example system administrators may wish to block all traffic between their network and undesirable destinations such as www napster com or other such leisure sites This can be achieved via firewall software Do not be surprised in the near future if some of your favourite internet destinations are no longer available from the computers in the IT suites or if certain types of software no longer function IT Services provide networked computers to enable students to complete their studies
One well publicised instance of choking involved BT s ADSL service This is an always on broadband service One of the main burdens on their network were the file sharing networks Some years ago BT decided to throttle such connections to only 5 kbytes s or so without telling their customers and denying any limitations when customers asked why speeds were so slow They were caught out and removed the limitations but have refused to promise not to re impose them at some point in the future
Firewalls and home computers the danger of always on
In the days when almost all home computer users were on a 56k modem and had to pay for their phone calls so online activity was limited few had a personal firewall However now that more and more have always on connections especially with a broadband connection they are now a major target for hackers In particular if a hacker can gain entry to a computer s resources they can use those resources to launch another attack and hence use that computer to gang up on the target In addition it is much easier for the hacker to cover their tracks thus making their detection by the police much more difficult
How personal firewalls work
To understand how a personal firewall works you need to understand about internet ports not a physical device as such but rather a virtual connection between a home computer and the network internet Different ports are used for different things For example email is usually received on port 110 but is usually sent on port 25 while ftp usually operates via port 21
A personal firewall examines all data packets and controls what can be sent to your computer or taken from your computer and which ports are used By blocking certain ports it prevents certain types of internet connection Thus blocking all traffic via port 21 will block all ftp activity involving your computer
If the personal firewall blocks all ports then the computer will effectively be shut off from the internet Thus it makes sense to block ports selectively Thus ports 31337 and 31338 are blocked since they are used by the Back Orifice Trojan Horse a type of hack that gives the hacker partial control over your computer
In addition a personal firewall can prevent a computer at a particular IP address from contacting you in effect as far as the computer at that IP address is concerned you are invisible
Proxy servers
A proxy server is a computer through which other computers access the sites that they wish to access One of the advantages of proxy servers is that you can have heightened security for that proxy server e g well maintained firewall software up to date email scanning etc and that will provide this high level of protection for all of the machines that access the network internet through it
Thus you might think that you are accessing an internet site directly but in fact you are accessing that internet site indirectly the proxy server intercepts your request to the internet site you are attempting to contact forwards the request on to the internet site intercepts the response and forwards that response on to you Both of the times in and out when it intercepts data it can check it to see if there is anything malicious in it
Web caches revisited
We have already mentioned web caches but they are in effect just a particular form of proxy server they intercept a request for a web page and offer you a locally stored version of it if that locally stored version is fairly recent
Big brother
The other thing that proxy servers can do is track what users do on the internet thus your ISP can track your online activity e g web sites visited files downloaded passwords used etc Law enforcement agencies in particular are interested in scanning the material that goes through proxy servers e g provide copies of all emails that mention the phrase Al Qaeda

Cookies and other invasions of your privacy
Ethics
One of the major issues that societies are having to come to terms with in this internet age is the right of the individual to privacy freedom from the prying eyes of online companies and others trying to garner information from you to enable them to generate higher profits
Such companies will argue that the internet will have no content if there is no possibility of profit and therefore it is in the interests of individuals to permit them to gather retain and use any personal information that they can convince us to type into their www forms
Cookies
Some of their tactics are perfectly reasonable at least at first sight for example many online sites place cookies on your hard disk when you visit them and provide personal information An example is www amazon co uk which when I enter the site automatically recognises who I am the cookie has my username and password in it and this information is automatically sent whenever I visit the www amazon co uk www site and so I am automatically logged in and bears that in mind when it sends me information it knows from past experience that I tend to buy British comedy DVDs and classic British film DVDs and so always has similar recommendations waiting for me this is possible because it has placed a cookie on my hard disk I have no problem with this and actually quite like it even though it does my personal finances no good at all
Thus far so good But who is to say that the company will not use the information in unacceptable ways For example what if Amazon co uk were to sell that information on to another company Or suppose that Amazon co uk was to read the cookies created on my hard disk by other online www sites The chances are that I would not know about this and even if I did what could I do not all internet sites are operated by firms located in countries with strong legal protection for the privacy of individuals
It is possible to turn off the cookies features in www browsers but this reduces the quality or ease of use of many www sites It is a trade off between the quality of your surfing experience and your right to privacy
Web tracking software
Far more worryingly is a type of software called web tracking software that permits the authors of that software to keep track of what people are doing online including which www sites they have visited Every so often the information is sent back to the software s authors This information can be sold to companies wishing the personal details especially email address and name of people with particular interests Thus if I visit a lot of personal finance www sites and this information is collected by the software then this information could be sold to companies involved in the personal finance business who are wanting to send email advertisements spam to create business for themselves
This kind of software is also called spyware The most in famous example of spyware is Go Zilla a download manager a program that allegedly speeds up your downloads from the internet When you install the program it will install the spyware without telling you and from that moment on your surfing habits are sent back to the company that wrote the software If you later uninstall the software the download manager is removed but the spyware remains Not nice
Spam
Spam is basically unsolicited junk mail Examples of too good to be true offers include
send 20 and I ll show you how to earn 25 000 a month working 10 hours a week from home honest
send 30 and I ll send you a device to that will make you overwhelmingly attractive to the opposite sex honest
send 40 and I ll send you all the porn you could ever want honest
send 250 and I ll let you take part in a scam to defraud an African country of multilateral aid and you ll make a minimum of 2 5m within 6 months honest
Sending junk mail through the normal post costs a lot of money perhaps 40p to 50p per letter Sending junk email is virtually cost free
How did they know that you wanted such offers They didn t They bought a list of 1m or 2m or 5m email addresses and have sent the same email to every email address on that list If you send an email to 1m people and only 0 01 are gullible enough to respond that is still 100 people to fleece And you can do it over and over again And since the internet is truly global then how can you get your money back if you ve been conned by someone from El Salvador or some such place and they left their temporary offices 3 months ago and they used false names and left an invalid forwarding address
How did the person that sold that list get your email address You probably signed on for access to a www site and that www site sold on the details
Spam mail can get so bad that there is little choice but to change your email address a real pain because you have to inform all of the legitimate people of your new email address
There is the ability to filter your email to block email from some sources but the email address of the sender is rarely the same and so only a limited amount of junk email can be filtered out
Encryption and other security issues
Encryption
Information can be sent across the internet that is very personal or very important from a personal finance point of view e g your credit card information Many people are very concerned about the possibility that this offers from online credit card fraud and consequently prefer not to shop online One way of improving security is the encryption of sensitive information even if people can get the information there is very little chance of them being able to interpret it
Basically with encryption the information is changed encrypted from the original form to another form and only the person to whom it is intentionally being send can transfer it back decrypt to its original form
For example my work email address is
p t seaman dundee ac uk
Applying ROT 13 encryption to it it becomes
c g frnzna qhaqrr np hx
In reality the internet uses much more secure encryption than ROT 13 but it illustrates the point
Digital certificates
Another problem encountered on the internet is knowing who sent you information Supposed that someone calling themselves Paul Seaman sent you an email containing a program called citass exe telling you that you needed to install it on your home computer in order to complete the next stage of the course How do you know it is from me email addresses can be forged In reality most of you would trust the sender and install it But what if it was a file called update exe and it allegedly came from Microsoft
One way to get around this problem is with what is known as a digital certificate This uses encryption to ensure as far as possible that the sender is who they say they are However most digital certificates are issued by private companies that few people have ever heard of and so for the moment at least we are still open to online fraud
Denial of Service Attacks
In recent years there have been several denial of service DOS attacks whereby the www sites of large internet companies Microsoft Amazon etc have been unavailable due to attacks by hackers
DOS attacks do not harm a computer or affect the data it stores but rather limit the accessibility of that computer to normal users it does this by swamping it with rubbish communications so much so that the computer can t deal with the proper requests for information
Most DOS attacks use what are known as PINGs Pocket InterNet Groper services yes really A ping is sent to a site which is in effect a message asking whether that site is connected to the internet The site will send a message back saying yes it is connected However the original ping message will typically have a forged return address the address will be that of the intended victim of the DOS attack and so the message will not be sent to the true sender of the message but rather to the computer which is the intended victim not only does this ensure that the victim is attacked it also provides anonymity for the hacker
The response to one ping message is easy for the victim site to deal with but millions of malicious ping response messages per second will deny normal users access to that victim site it is simply overwhelmed
If the original ping is correctly constructed it can be sent to an ISP which will automatically pass it on to all its online customers and so each of them will send back a response message to the forged address Thus one such ping sent to Telewest could result in tens of thousands hundreds of thousands of response messages There is software to prevent this taking place but the software can only provide so much protection if the hacker uses a new technique then the software might not have the necessary protection built in
For a DOS attack to take down a major www site requires that the attacking computer s have sufficient bandwidth to overwhelm the server it is attacking Given that most attacked servers are major systems operated by major organisations this is unlikely Therefore most DOS attacks are actually Distributed Denial Of Service attacks DDOS attacks whereby the hackers take over a large number of computers and use those computers to launch a concerted attack on their intended victim This type of concerted attack is possible due to hacker tools such as Trojan Horses
My IP address is 134 36 98 1 while the IP address for the university web site home page actually stored on the server duxweb dundee ac uk is 134 36 2 84
A Trojan Horse is a program that once run will install itself on your computer and permit the hacker that sent it to you to issue commands remotely that your computer will obey But this requires you to permit the installation of the program on your computer One of the most frequent ways in which this is done is via the victim opening running an executable file enclosed as an email attachment you have been warned Once Back Orifice is installed running on your computer it will open ports 31337 and 31338 to hackers Hackers can use a port scanner to find internet connected computers running Back Orifice and take them over for whatever purpose they want you may not even realise that this has happened
Many spam emails contain information about being removed from the list NEVER ever choose this option since it simply confirms that your email address is still in current use Using this feature is almost guaranteed to massively increase the quantity of email being sent
Some proponents of online shopping argue that the same can happen when you make an order over the phone However the nature of the internet involving powerful computers means that a lot of snooping can be done with very little human input Thus intercepting communication between your computer and an online store is much more profitable to a fraudster than trying to listen in on phone calls made to a mail order firm
Hacker is a term with a specific meaning gaining unauthorised access to a computer but in general it is used to indicate someone who attempts to prevent a computer functioning properly
Communication and Information Technology in the Arts and Social Sciences
15 Networks in more depth
Faculty of Arts and Social Sciences University of Dundee
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