A pirated version of Windows 7 Release Candidate infected with a Trojan horse has created a botnet with tens of thousands of bots under its control, according to researchers at security firm Damballa.

The software, which first appeared on April 24, spread as quickly as several hundred new bots per hour, and controlled roughly 27,000 bots by the time Damballa took over the network's command and control server on May 10, the firm said Tuesday.

The pirated software was spread via popular pir...