A new Trojan horse demands a $10.99 ransom payment to stop erasing files on the infected PC's hard drive, a security firm said Thursday.

According to U.K.-based Sophos, the Ransom.a Trojan freezes the computer, then puts up a message saying it will delete files every half hour until the user sends $10.99 via Western Union to a designated account.

In the message, the blackmailer claims that anti-virus software cannot retrieve the deleted files, that the traditional Ctrl-Alt-Del key combination won't unstick the computer, and that the "ransomware" runs each time Windows boots.

When the user presses Ctrl-Alt-Del, the malware pops up another message.

"Yeah, We don't die, We multiply! Ctrl+Alt+Del isn't quite working today, is it? I'm not the sharpest tool in the shed but Crtl+Alt+Del is everyone's S.O.S."

So-called "ransomware," malicious programs that threaten to destroy or lock up data, are still relatively rare, although this Trojan is the second in the last five weeks.

In mid-March, a different Trojan, called "Cryzip" and "Zippo.a," demanded $300 in return for a password that would free users' files from maliciously-made ZIP archives. Multiple security companies, however, quickly figured out the password.