Every since the dawn of computing and users started to write their own software there has been there have been viruses however it wasn't until the 1980s that the potential threat of computer viruses became common knowledge. The action of a virus is not too dissimilar to that of its name, it is a small computer program that makes its way onto a computer with the aim of duplicating itself and infecting other computer systems. Although a virus doesn't have to have bad intentions it is unfortunate that almost all of them have.

In the past viruses would spread by hiding within files downloaded from bulletin boards or on floppy disks used to store and transfer documents. As computer technology advanced the introduction of computer networks, the internet and email provided ample opportunities for a virus to spread amongst systems. Initially a virus makes its way onto a computer in the form of a trojan.

A trojan, taken from the term trojan horse, is essentially a file or program that appears appealing enough for somebody to download it or execute it. Hidden within this file however is a virus which once activated spreads onto the host computer system and hides. Once it has infected the system the virus can set about spreading amongst files and applications and can even utilise existing network and internet connections to reach as many other computers as possible.

Virus Types:

Although countless viruses exist they can generally be categorised into one of the following:

The potential power of a virus or worm should never be underestimated as was proved on July 19th 2001 when the Code Red Worm managed to replicate some 250,000 times in under 9 hours. The Code Red worm was written to take advantage of a security bug in Windows NT4/2000 servers running Microsoft Internet Information Server versions 4.0 or 5.0. Although Microsoft had released a security patch for the bug the Code Red worm scanned the internet looking for systems that hadn't applied the patch. The worm then duplicated itself onto the unprotected server and from there continued to scan the internet for further systems it could infect. The effect of Code Red was so destructive and caused such an impact in performance on the internet that some ISP had to temporarily disable internet access for infected customers whilst they informed them of the problem and what they needed to do to rectify it.

By far the most effective way of keeping your system safe is to run some form of Anti Virus software which is a piece of software that is installed onto a computer system with the purpose of monitoring all files and data which are read from or written to any of the systems devices, memory or network connections and also emails as the are sent and received accross the internet.

By monitoring all data transfers and comparing them to its database of known viruses, the software is capable of detecting a virus, worm or trojan based on its data signiature or by other traits that have been recorded. Once detected the virus can be removed and any infected files can be cleaned or confined before the virus has a chance to spread. Similarly, if the virus is detected in memory then that portiion memory can be isolated and cleaned. If an infected file is found and it cannot be cleaned then it may be necessary to quarrantine and delete the infected file to ensure that the virus cannot spread.

So What Precautions Can I Take?

Since Anti Virus programs work by monitoring data transfers and comparing them to its database there are two main factors which will help ensure maximum protection. The first is that the Anti Virus program must be running at all times so that viruses can be detected as soon as they enter the system rather than after they have spread. And secondly the virus database must be updated regularly as new viruses are detected almost daily and if the virus isn't listed in the database then it is unlikey that the Anti Virus software will detect its prescence.

There are many leading Anti Virus programs on the market today and most come with 6 months or 1 year of free updates. As well as protecting the system with Anti Virus software the user should always ensure floppy disks are write protected if they are only being read from, that email attachements are not opened unless they come from a trusted source, and that all files downloaded from the internet are scanned throghly before opening them.