To defeat a malicious botnet, build a friendly one

Beating the "botnets" – armies of infected computers used to attack websites – requires borrowing tactics from the bad guys, say computer security researchers.

A team at the University of Washington, US, want to marshal swarms of good computers to neutralise the bad ones. They say their plan would be cheap to implement and could cope with botnets of any size.

Through such means as web pages and viruses, hackers spread malicious software that lets them create and manipulate "zombie computers", leaving owners of the infected machines none the wiser.

Botnets are networks of these zombies and are used to send spam or launch distributed denial-of-service (DDoS) attacks.

These attacks can cause internet servers to crash by overwhelming them with information requests from a botnet's computers. They are so commonly used to extort money from website owners that the practice is dubbed "the street crime of the web".