How to defeat hidden computer menaceE-HELP: James Catchpole and Simon Walker on a step-by-step anti-virus guide We have all heard of the now infamous computer viruses, such as the Love Bug, Melissa and the Anna Kournikova virus.

More than 40,000 active viruses are known, with approximately 1,000 more being found each month.The resulting costs of virus attacks, often unreported to save embarrassment, means the financial cost to businesses is incalculable, though it is thought to be in the hundreds of millions of pounds.

Means of entry for viruses is often through lapses in computer security and complacency.

These include such things as back doors, which access short cuts installed by your computer engineers, or more disturbingly, by computer hackers to guarantee themselves a permanent path into your system.However, viruses enter computer systems through apparently harmless channels.

Viruses are hidden, pretending to be intriguing video-clips or love-letters which, once opened, are activated to infect your systems, and often sneak into your computer on the backs of e-mails from people you know.Viruses can act dramatically or subtly, but all with one intent: to damage computers, files, applications and networks.

Trojan horses, like their Greek namesake, offer themselves to you as something good, but once inside read or destroy files, or plant new ones.Logic bombs, often riding inside Trojan horses, hide themselves, waiting to explode at some preordained time, or upon some trigger event.

There are also worms, which replicate and expand to cripple systems by over-running them with useless data.

The most malicious, macro viruses, are often inadvertently executed, running an automated series of events, damaging data files, document templates or spreadsheets, while they are open.Viruses may also transmit data.

Your most valuable and confidential files could be sent to anybody and everybody in your electronic address books, courtesy of Melissa.

Breaches of confidentiality such as these could easily ruin a firms reputation, and possibly the firms client relationships as well.

Not the way to endear yourself to clients.As a consequence of the proliferation of viruses, measures to prevent attack are ever more vital.

The following should be considered: l Several regularly updated anti-virus software programs should be used one alone is not enough.

These should be set up to check every incoming file and e-mail and every application which is activated;l Clear guidelines on Internet use and e-mail should be exercised and monitored and staff awareness of the potential dangers of viruses should also be increased;l Your entire system should be separately backed up at regular intervals and stored off-line; no matter how good your defences are, there is always the chance that something will surmount them and cause some harm;l If a third party is supporting your systems, check that they also have similar and state-of-the-art defences, and;l Keep your procedures and policies under continual review to ensure that no new viruses or technologies outpace your defences.James Catchpole is a member of the IP, IT and digital business group, and Simon Walker is head of e-business, at Landwell UK