The popularity of email, however, may soon be rivalled by a newer and more nimble online communications system, Instant Messaging (IM).

At last count, there were 50 million IM users worldwide. Its exploding popularity threatens to open a range of new security issues - issues that the anti-virus and internet firewall vendors have been slow to address.

IM is like email on steroids. Users hold online conversations in real-time, passing typed messages back and forth in a way similar to speaking on a telephone. IM software tells users who is online and provides for conferences between multiple participants. In a corporate setting, this has, in many instances, filled the gap between email and telephones, providing fast collaboration between many people in different parts of the business.

Elsewhere, IM has become the latest toy of internet consumers, many of whom are enamoured of its recreational potential but ignorant of its potential dangers.

In recent years email has been the preferred target of hackers. As virus infections have affected an increasing number of ordinary email users, the adoption of email antivirus packages such as Norton, by Symantec, Vet, from Computer Associates, and McAfee, from Network Associates, has become increasingly common. The increasing popularity of IM over the past two years threatens to take security breaches to a new level.

The four most popular IM products in use outside the commercial world - MSN Messenger, Yahoo Messenger, AOL Instant Messenger and ICQ - are all free and all highly vulnerable to security breaches. They allow users to freely transfer potentially virus-ridden files and to conduct unencrypted chat sessions that are a virtual open book to any reasonably knowledgeable hacker. The security vendors, however, appear to have lagged behind the IM popularity curve and this is an issue weighing heavily on the minds of corporate users.