Updated Virus writers are exploiting machines infected by MyDoom-A to launch a denial of service attacks on Microsoft with the release of yet another Net worm.
The Doomjuice worm, discovered yesterday, uses the back door installed by Mydoom-A to spread. Doomjuice does not propagate using email.
Doomjuice (AKA MyDoom-C) scans random IP addresses to locate machines with the MyDoom-A backdoor (TCP port 3127) open. Using this technique it infects vulnerable machines that then becomes doubly infected.
Zombie machines infected by MyDoom-C become part of a DDoS attack against Microsoft.com - explained in greater depth here. Doomjuice - unlike MyDoom-A - is not programmed to attack www.sco.com.
A second worm, Deadhat, removes the MyDoom virus from its victims, installing itself instead. This worm spreads through the back door opened by MyDoom-A and MyDoom-B as well as through a P2P application called SoulSeek.
Worms infected by Deadhat are - like those infected by MyDoom-A - still under the control of crackers. More info on Deadhat (AKA Vesser) can be found here.
Neither Deadhat nor Doomjuice are spreading particularly quickly. AV vendors rate both as relatively low-risk. MyDoom-A, due to deactivate on Thursday, remains the real menace.
As usual, all these worms are Windows-only - Linux, Mac, OS/2 and Unix users are immune.
Windows users meanwhile are left to shelter under the projection of AV scanner software until the current MyDoom squall dies down. Even security conscious PC users or Mac users are not wholly immune though, thanks to the blizzard of bounced and redirected messages generated as a result of MyDoom's spoofing behaviour. ®
The Doomjuice worm also plants a copy of the source code for MyDoom-A onto infected computers, according to AV vendor Sophos. The company reckons this is either an attempt to encourage others to write copy-cat viruses or in an attempt to make it more difficult to catch the true author of the worm, if that person is ever apprehended.