Microsoft to target other botnets with legal weapon

As a fall-back, Waledac bots can communicate to their controllers "indefinitely" using IP (Internet Protocol) addresses that are hard-coded into the bot Trojan, SecureWorks' Stewart said last week.

Campana acknowledged those alternate command-and-control links within Waledac, and said Microsoft is attacking those as well. He declined to provide details of what Microsoft was doing, or when — or even if — the Waledac bots would be unreachable by their makers. "In addition to the legal action against the domains, we have taken other technical measures," said Campana. "At this point, we're still working that angle and actively adapting our measures."

Several message security and spam filtering companies and organizations, including Google 's Postini and the UK-based SpamHaus, also disputed Microsoft's claim last week that Waledac was a "major distributor of spam" and that crippling it would reduce spam.

Symantec's MessageLabs also weighed in on the impact issue, and like other vendors, downplayed Waledac's significance. "There's been no real noticeable effect of the takedown," Matt Sergeant, a senior anti-spam technologist with MessageLabs, said in an email. "It's one of the smallest botnets out there, and the court order appears to have had very little effect on its output."

Microsoft countered, saying it's too early to gauge its anti-Waledac moves. "We're still looking at the impact this has had," said Campana, referring specifically to the monitoring Microsoft's doing of the volume of spam addressed to Windows Live Hotmail accounts. "It's somewhat premature to say 'yay or nay' yet." The next one or two weeks will tell the tale, Campana agreed.

But Boscovich would not promise that Microsoft would make Hotmail spam data public. "We'll look at that [decision] fairly soon," he said.

It isn't the first time that Microsoft has said it has crippled a botnet built by this group of hackers. In April 2008, the company took credit for crushing the Storm botnet — Waledac's predecessor — saying that the malware search-and-destroy tool it distributes to Windows users every month disinfected so many bots that the hackers threw in the towel .

As with the Waledac take-down, researchers at the time disputed Microsoft's claim that it had beaten Storm into submission.

Campana urged Windows users to run the Microsoft-made Malicious Software Removal Tool (MSRT) to scrub Waledac from infected systems, and up-to-date anti-virus software to keep it off still-clean machines. "This is definitely a preventable issue," he said.