A new version of the Doomjuice worm has been released into the wild in an apparent effort by hackers to modify an attack against Microsoft's Web site.

Doomjuice-B attacks www.microsoft.com, much like its predecessor Doomjuice-A, but now it sets random HTTP headers to make it more difficult to filter out the attack traffic. Its assault begins tomorrow.

TDoomJuice-B is smaller in size than DoomJuice-A because it does not drop the source code of MyDoom-A. AV vendor F-Secure reckons DoomJuice-B is slightly more virulent than its predecessor.

Netcraft estimates the scope of the "zombie" network potentially commanded by DoomJuice-B is likely to be smaller than the original pool of MyDoom-compromised machines which has kept www.sco.com offline with a DDoS attack since the start of February.

Both variants of Doomjuice use a backdoor left open by MyDoom-A to spread, instead of propagating through email or P2P file-sharing networks. Neither versions attacks SCO's Web site.

MyDoom infected anything between 400,000 and one million PCs, according to sundry estimates. Yesterday more than 65,000 IP addresses were actively scanning to and from port 3127, the backdoor left open by MyDoom_A, according to he SANS Institute's Internet Storm Center. This suggests that many users have cleaned up their act.

Netcraft has published a chart showing the performance of all the sites involved in the MyDoom/DoomJuice DDoS attacks here. ®

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