Summary
The Zindos worm used the backdoor that was installed by the Mydoom.M worm, that spread earlier. Since Zindos had no other infection vector, so it could only spread to computers that were infected with Mydoom.M earlier. It even used a list of infected computers, collected by Mydoom. I suppose the idea was to use the mass-mailing worm to pave way to the payload for rapid distribution later. The Zindos code had not much to do, just go straight through the list of already compromised computers and copy itself there through the backdoor. Zindos is a network worm which spreads with the help of the Mydoom.M mass-mailing worm. More information on Mydoom.M is available at http://www.f-secure.com/v-descs/mydoom_m.shtml