A new version of the Sober worm was unleashed last night, with the timing chosen to correspond with the founding of the German Nazi party and a major German political conference starting today.
There are no early reports of major problems, but firms have been warned to monitor the situation.
A warning about the attack was issued by security software companies at the end of last year, after it was discovered that the previous version of Sober had been programmed to trigger new attacks on the internet.
Those under threat from the latest worm are users that did not patch their systems against the previous version of Sober.
Microsoft has issued an advisory about the latest version and has warned that another triggered Sober attack is set for two week’s time, and every two weeks after that.
Companies are already dealing with a critical graphics flaw in the Windows operating system, for which Microsoft issued a patch overnight.
The Sober worm is believed to have been developed in Germany, and both English and German language versions of the worm are usually spread with each variant.
Sober first appeared in 2003 and is one of the most virulent worms to have ever appeared.
The worm is spread via e-mail attachments and attempts to turn off users’ security settings. It also leaves a backdoor that can be used by remote hackers to run arbitrary code on users’ machines.
Sober replicates itself via infected users’ e-mail address books and can cause networks to crash under the volume of traffic created.