"Code Red" worm claims 12,000 servers - Tech News - CNET.com
"Each instance of the worm will attack the same computers in the same order, according to eEye's analysis. Maiffret said that while the addresses of the computers attacked by the worm seem to be random, because the worm uses the same starting point, or "seed," to generate the list, the "random" lists that any two worms generate are identical. Like identical genes, which produce a clone, identical seed numbers produce attack lists that are the same."

This also means that anyone who has access to an infected computer can generate the attack list and thus know the addresses of all the other infected computers.