The e-mail, entitled 'Microsoft Security Bulletin MS07-0065' purports to come from the software giant but has actually been sent out by hackers.

It describes a bogus problem with the Outlook e-mail programme and directs readers to link to download a patch. However, the link leads to a compromised website containing a Trojan horse virus.

A spokesman from Sophos, the security software company, said:

"The irony is that as awareness of computer security issues has risen, and the need for patching against vulnerabilities, so social engineering tricks which pose as critical software fixes are likely to succeed in conning the public."