Top ten viruses for April

The problem with Magistr is that it can mass email through any email program as it contains its own SMTP handler. Having gained access to a user's hard drive Magistr will render the hard drive and BIOS of a computer dead.

Peter Cooper, UK head of technical support at Sophos, urged users to keep an eye on internet updates of AV software.

Cooper added: "Magistr relies on users to open emails. If you're not expecting an email off someone, delete it immediately, it's just not worth it."

The Kakworm virus that exploits a fault in the MS Outlook Express program, and Hybris viruses, another that spreads over email, were second (14 per cent of reported infections) and third (12.6 per cent) respectively.

A notable entry to the top ten this month is the Badtrans worm that has also been upgraded to level four by Symantec due to an increase in the number of submissions.

Discovered on 11 April, it replies to all unread mails in your email message folders, and drops a backdoor Trojan in the \Windows folder.