Just when you thought it was safe to go back onto the internet, your email spam may have unknowingly been sent by you.

Unsolicited commercial mailers have taken to using Trojan horse methods of infection to set up spam safe houses -- similar to distributed denial of service (DDoS) attacks.

The latest fears have arisen from a report initially published on SecurityFocus.com. According to the report, Trojan 'zombies' arrive by spam email and use social engineering methods to propagate itself with convincing email headers. The rogue software installer contains either an integrated SMTP server or installs random open proxy protocols allowing a remote user to connect and begin the bulk mailing.

The latest spam zombie, 'Proxy-Guzu' which surfaced last week sends a confirmation email to a Hotmail account with the infected machine's IP and open port, leaving it vulnerable for taking control of and spamming. Ever decreasing options means the spammers have been forced to seek alternative methods of distributing unwanted messages and advertising.

Although spam is still legal, using someone else's computer to send an email to someone else isn't. But unlike other forms of spam, the attacker is untraceable. Margie Arbon from anti-spam group MAPS is quoted in the report saying its 'untraceable' behaviour means any efforts to trace the source will reveal only the victim's Internet address.

"It's untraceable. I hate to put that in print, but it's the truth," said Arbon

You can find more information about spam zombies here.