Once-prolific Pushdo botnet crippled

Security researchers have disrupted the botnet known as Pushdo, a coup that over the past 48 hours has almost completely choked the torrent of junkmail from the once-prolific spam network.

Researchers from the security inteligence firm LastLine said that they identified a total of 30 servers used as Pushdo command and control channels and managed to get the plug pulled on 20 of them. As a result, the torrent of junkmail spewing from it dropped to almost zero on Thursday, according to figures from M86 Security Labs.

Also known as Cutwail, Pushdo has long maintained a strong presence in the rogues gallery of the security world. It is known for spam that attempts to trick recipients into installing malware and it also excels at hiding itself from intrusion-prevention systems, security researches have said. Its output has varied over the years with estimates as high as 20 percent of the world's spam at some points.

Pushdo was also notable for other technical feats, including its ability to pierce Microsoft Live by defeating its audio captchas.

Last year, federal authorities shut down a host provider known as 3FN, which was believed to be a major provider for Pushdo, but spam levels didn't drop. Researchers surmised then that spam zombies continued to churn out junkmail based on old instructions until new command and control channels were being set up. It's unclear why spam levels dropped this time and not then.

The disruption is good news, but it also highlights the uphill challenge white hats face in severing menaces from the net. Some of the host providers contacted by LastLine ignored the request to disconnect the malicious servers, despite receiving a fair amount of data documenting their bad deeds. ®