A fake Microsoft security bulletin is doing the rounds, complete with a link to a Trojan that will hand over control of your PC.

The e-mail identifies itself as Microsoft Security Bulletin MS05-039, and offers a link to what it claims is a patch against the Sober Zafi and Mytob worms.

Bulletin MS05-039 doesn't exist however and a phony patch is a variant of the SDBot Trojan software, which is at present not detected by anti-virus software products, according to a report form security research firm WebSense.

The risk is low right now however, because the server hosting the Trojan downloads no longer appears to be active. That server, hosted by ThePlanet.com, exceeded its allowed bandwidth and was shut down

A fundamental mistake, but one that will most likely not be repeated in future.