Experts yesterday warned of a new computer virus which attacks antivirus software and firewalls in a bid to access your personal details.

Bugbear is an internet worm with a Trojan horse — in other words a destructive program masquerading as a benign application. It attempts to get into your email system in order to glean personal information from your messages. It can also track what you type into emails using a keylogger to capture your keystrokes.

The bug has been labelled medium risk by experts at Network Associates. The security company claims the virus is attacking users of older versions (5.01 and 5.5) of Microsoft's Internet Explorer.

Believed to have originated in Malaysia, Bugbear spread throughout the US via a vulnerability in Outlook that executes attachments automatically.

"It uses open file shares like Funlove, drops a keylogger like Badtrans, and is a mass-mailer like Klez. What is interesting about Bugbear is that it tries to turn off your antivirus software or firewall, and then inserts a keylogger which captures your keystrokes as you type and sends them to a TCP/IP port," Allan Bell, Network Associate's marketing manager told news website, Silicon.

The worm is disguised as an email and the only way to detect it is through the attachments which are always 50,688 bytes in size.

Antivirus firm MessageLabs said it has intercepted "around 9,000 incidents in just two days".

All versions of Windows are vulnerable, but the worm does not affect Macintosh, Unix or Linux platforms.

Anyone who suspects they have been infected by the virus can contact MessageLabs directly on 01452 627 627.