Spammers are turning to file-sharing scare tactics in which they con innocent broadband users into thinking they have been accused of illegal activities, Trend Micro has found.

Researchers at the internet security firm say that users are sent an email threatening them with interrupted Internet connectivity or legal action unless they open an attachment.

When they do so, the file turns out to be malware.

"Recipients are most likely to be motivated by fear to fall for this ruse," said Macky Cruz of Trend Micro.

"It is, after all, the internet surfer's worst nightmare to have all their Internet activities known to other parties - especially those who threaten legal prosecution."

Last month, senior threat researcher at Storm Worm, David Sancho, discovered a spam run that told users about the FBI investigating possible terrorists in the popular social networking site Facebook.