Emailed messages containing links to a download which claims to fix a flaw in Windows XP Service Pack 1 and Service Pack 2 are actually malicious programs.
The warning comes from security firm Trend Micro, which warned surfers to be on their guard against the trick.
Messages appear to come from Microsoft and direct you to a website where you can download a patch. However, what you will actually download is a Trojan.
"Spammed email messages were found pretending to come from Microsoft Windows Support and claiming that Windows XP Service Pack 1 and Service Pack 2 have been discovered to have an error that can damage the computer's software or even the hardware," said Maydalene Salvador of Trend Micro.
The Trojan monitors online banking transactions and steals login data when you visit a bank's website.
Trend Micro said that its security software was already protecting against the Trojan and it was also blocking the spam mails linking to it.