Operating under the theory that if you kill the head, the body will follow, a group of high-profile security researchers is ramping up efforts to find and disable the command-and-control infrastructure that powers millions of zombie drone machines, or bots, hijacked by malicious hackers. A botnet, which is short for “robot network,” is a collection of broadband-enabled computers that have been commandeered by hackers for use in spam runs, distributed denial-of-service attacks or malware installation. The compromised machines are controlled by a “botmaster” via an IRC (Inter Relay Chat) server installed illegally on a high-bandwidth educational or corporate network. “If that command-and-control is disabled, all the machines in that botnet become useless to the botmaster. It’s an important part of dealing with this problem,” said Gadi Evron, a botnet hunter who helps to manage the anti-botnet fightback.