Hackers are attempting to infect PCs with malware using a 'long-lost female school friend' to lure gullible internet users, a security vendor has warned.

Cyber-criminals are taking advantage of the current popularity of social networking and online friendships among adults, according to Sophos.

The emails purport to be from a young blonde woman called 'Ann Berns' who claims that she went to school with the recipient.

Graham Cluley, senior technology consultant at Sophos, said that it is a sad state of affairs when cyber-criminals need little more than a picture of a blonde woman with pigtails to steal passwords from unwary internet users.

"The lonely, the randy or the just plain curious might be tempted to click on the link, but they risk falling straight into a trap set by hackers," he said.

Clicking a link to the 'Ann Berns' personal homepage leads to a Trojan horse designed to break into online accounts and commit identity theft.

The email reads: 'Hi! I'm not sure if you remember me. I'm Ann Berns, I guess we went to high school together. Do you want to see what I look like now? Visit my home page then.'

Cluley warned that all internet users need to take more care over unsolicited emails, and ensure that they are properly defended when they open their email inbox or surf the web.

"People need to think with their heads, not with their loins," said Cluley. "The use of attractive young women to infect the lovelorn is far from a new trick, but it seems to work time and time again."