Watch out for a virus which poses as a security fix for the infamous MyDoom worm.

Sober-D arrives in the form of an email with the subject line "Microsoft Alert: Please Read!" and an attached Zip file with a malicious executable. Users who are duped into running this payload get their PCs infected by the virus and contribute to the further spread of the worm.

Sober-D, first spotted this morning (8 March), is spreading, albeit on a modest scale. Most anti-virus firms rate it as a low-to -medium risk. Once again, this is a Windows-only menace.

The worm is far less of a problem than its predecessor, Sober-C, which spread extensively last October. Germany was hit particularly hard because people were fooled by the unusual use of their native language in the message accompanying the worm.

Last week, Magdeburg University research group AV-Test.org published research to establish the reaction time of anti-virus developers to new malicious code. It focused on activity surrounding the Sober-C outbreak.

The research found AV vendors took between 10 hours to three days to produce signatures to detect the virus.

Sober-D is a medium-level outbreak and AV vendors would doubtless react quicker to another MyDoom. But Magdeburg University's research, the first of its kind we've come across, illustrates once again the reactive nature of AV technology. Until supplementary or alternative technology is widely adopted to combat fast-spreading worms, Windows viruses will continue to be a daily nuisance. ®