Removing zombies from customers' computers is a difficult problem. See
Spam Zombies And Inbound Flows To Compromised Customer Systems
Joe St Sauver, Ph.D., MAAWG Senior Technical Advisor
MAAWG General Meeting, San Diego, March 1st, 2005
http://darkwing.uoregon.edu/~joe/zombies.pdf
This paper describes some of the defensive strategies zombie writers are using to block attempts at removal, leaving only the "nuke-and-pave" option, which for most customers is unacceptable. The FTC is now pushing "Operation Spam Zombies" telling ISPs to "... provide, or point your customers to, easy-to-use tools to remove zombie code if their computers have been infected, and provide the appropriate assistance." http://www.ftc.gov/bcp/conline/edcams/spam/zombie/index.htm There is no suggestion as to where we might find such tools.
If the FTC wants to spend money to clean up zombies, I can suggest a better strategy. Put out a reward for the best "Zombie Neuter" program. The same perverts who are now writing programs to hijack other zombies for their own spam clients, could write a program to hijack and neuter the zombies. The incentive will be not just the money, but the fame and glory from winning the contest!!
This program could be used by ISPs in addition to blocking port 25 and all the other well-known ISP "best practices". Any user system that is open for spammers would also be open for a benign patch. "Sorry, your mail has been blocked, because your system has been infected with a mail worm. <Click Here> to install a patch on your system and re-activate your account." Of course, there would need to be some user education follow on, and stricter measures if it happens again.
The program I have in mind would not have to completely clean the infected computer, just render it harmless. This will require that it overcome the defensive strategies discussed in the paper above. The programmers best qualified to do this are same the pimple-face nerds who are now developing these strategies.
The winning program must be open source, and the reward is forfeited if someone discovers a back door.