My security colleague, Joris Evers, reported on News.com about to hide their networks within real-world traffic.
Botnets are groups of compromised desktop computers (zombies) which, in large numbers, can be used
to attack corporate networks, or
to make profits from click-to-view Web advertising. Botnets are typically controlled via Internet Relay Chat (IRC) commands, but as Joris discovered, some are now using Web-based techniques, making detection much harder.