What is the best way to ensure that my computer doesn t pick up a virus

A. There is no sure way of ensuring that your computer remains virus free, but you can install an anti virus program (or several programs) as a precaution. A virus' main aim is to get onto your computer, replicate itself and then spread onto other computers - so it is likely to be carried on a floppy disk, CD or via the Internet usually on an email, so it is important that any virus protection program you install scans these outlets.

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Anti virus software can be either on-demand (which means you choose to have it scan a disk etc) or on-access (it checks files automatically as you open them). While it is good practice to have more than one anti-virus program on your computer, it is not advisable to have two on-access scanners running at the same time as two scanners trying to scan a file simultaneously can confuse your computer.

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Q. How often should I install virus protection software

A. As viruses are written all the time it is difficult to ensure that you're protected all the time, but if you update your software every six months or every year (free updates are usually available via the Internet) then you should be able to work relatively safely.

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Q. How does anti virus software work

A. A good anti virus software package will use a combination of techniques to detect a virus. One such technique is pattern matching (used to attack known viruses) whereby the anti virus program scans a file by looking for a sequence of bytes within the programme code (called a fingerprint or pattern) which uniquely identify the virus. But as there are thousands of viruses out there it is not an efficient technique on its own. In addition to this, a number of polymorphic viruses exist which rearrange the code bytes of a virus each time it infects a file, or use encryption that can make detection even more difficult. The pattern matching technique is very thorough, but it only detects viruses it knows about, so are always out of date.

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It is best to run an anti virus program that can also detect unknown viruses, this type of software will check files via inoculation - basically it checks whether a file has changed (all files will change when infected). This system also has some limitations in that it does not always detect macro (see below) viruses.

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Heuristic scanning is another method of attacking a virus, and is the best method of detecting macro viruses as its software analyses the program code to see if it has any features common to known viruses, the more common features found in a scan the more likely it is to carry a virus. All leading anti viral programmes will use a combination of these methods to detect viruses.

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Q. What types of viruses are out there

A. Although there are thousands of viruses written, these usually fall into three types of virus - Trojan horses, macros and worms.

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A Trojan Horse installs software onto your computer which allows someone else access to information on your computer, from another computer.

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Macro viruses hide within computer software that have macros eg. word processing and spreadsheet software, and are activated when you open files.

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A worm virus is self replicating. It copies itself continuously on your computer and uses up the memory, and can attach itself to email, and automatically mail your entire address book.

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Q. Can you recommend some good anti-virus software

A. The leading names in virus protection are Symantec and McAfee (updated versions of old software and new virus protection programmes are continually launched by both companies), although other cheaper virus protection programmes are available on the market.

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Symantec's new Norton Anti Virus 2001 software is very good and costs about �30, it is very easy to install and automatically checks for fresh viruses when you log on to the Internet.

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McAfee Virus Scan 5.11 is a good programme, but you really need to have some computer knowledge to install it, this is easy but not a good tool for absolute beginners. It costs about �24.

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Grisoft 's AVG Gold Anti Virus software costs �20 and comes with two years free updates.

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Alternatively, If you want to be completely up-to-date with your virus protection it is good to check out some anti-virus websites. These include:

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http://www.symantec.com

http://www.mcafeeb2b.com

http://antivirus.cai.com

http://www.cknow.com

http://www.pchell.com

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Q. Do you have any tips for avoiding viruses

A. Common sense should prevail, but it is good to know that most viruses won't start working until they are switched on. As these are often sent via email the best way to avoid kick-starting the virus is to delete any suspicious email and not open them. In general avoid opening any attachments if you don't know who the email is from.

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By Karen Anderson