Researchers question Microsoft's botnet take-down

No change in spam volume after Microsoft claims it crippled Waledac

A prominent security researcher today said he doubts Microsoft's take-down of the Waledac botnet would have any impact on spam levels, as the company claimed.

"Waledac just is not a hugely prolific spammer," said Joe Stewart, director of malware analysis at SecureWorks and a noted botnet researcher. "So I don't think it's going to affect spam [volume]. What it does do lately..., what it's used for, is to install rogue antivirus software."

The U.K.-based anti-spam service Spamhaus echoed Stewart today. "If [Microsoft's take-down] did affect spam, we haven't noticed," said Richard Cox, the chief information officer at Spamhaus. Like Stewart, Cox also dismissed Waledac's threat as a spam engine.

"Waledac was not a high threat, it's less than 1% of the spam traffic," Cox said. "What we're worried about is Zeus, which is a far more damaging botnet, which is creating a substantial amount of spam."

Postini, the message security and filtering firm owned by Google, also said it had not detected any drop in spam. "The team hasn't seen any change so far," said Google spokesman Jay Nancarrow.

Earlier today, Microsoft said that the Waledac botnet, which it claimed controls hundreds of thousands of infected PCs -- is a "major distributor of spam globally." Microsoft also said that its researchers had snatched about 60,000 machines away from the botnet.

Stewart wasn't seeing any evidence of those claims, either. "I haven't seen any decrease in [Waledac's] activity, the researcher said. "To me, it looks like business as usual."

Late Wednesday, Microsoft announced it had won a federal court order that cut off 277 .com domains associated with the botnet, and said that by knocking those sites off the Internet, it would seriously disrupt Waledac's operation. "This action has quickly and effectively cut off traffic to Waledac at the '.com' or domain registry level, severing the connection between the command and control centers of the botnet and most of its thousands of zombie computers around the world," Tim Cranton , an associate general counsel with Microsoft, said in a blog entry yesterday.

But Stewart said it's very unlikely that the move had actually crippled the botnet. "Waledac uses a peer-to-peer protocol for its command and control," he said, referring to the mechanism that the most technically-advanced zombie PC commanders use to control their armies. "But the bots don't really [depend] on those domain names to communicate."

In fact, said Stewart, Waledac bots will be able to communicate "indefinitely" by using the IP (Internet Protocol) addresses that are hard-coded into the bot Trojan. To kill off a botnet like Waledac, Microsoft would have had to target not only the domains it did, but also every possible IP address coded into the malware. "I don't see how you can kill a botnet like this," Stewart said. "There's no single point of failure for these botnets."

Even so, he applauded Microsoft's move. "...This is a good start, it's a good step in the right direction," Stewart said, offering up other ways the company's resources might have been better spent. "There are plenty of other botnets where this approach might work -- any that depend on a centralized command and control server."

Waledac was created by, and is maintained by, hackers who previously flooded the Internet with the Storm bot Trojan. The people behind this botnet aren't rookies, Stewart said. "We're dealing with the same people behind Storm, and they definitely know the ins and outs."

In all likelihood, he added, Microsoft's maneuver won't stop an established botnet like Waledac. "They're attacking the very, very front end of the whole scheme of the bot," he said.

Microsoft acknowledged that its work isn't done. "[This] is not a silver bullet for undoing all the damage we believe Waledac has caused," said Cranton. "Although the zombies are now largely out of the bot-herders' control, they are still infected with the original malware."

Message security companies that monitor the pulse of spam, including Symantec's MessageLabs and Google 's Postini, were not able to immediately come up with data to show whether the purported demise of Waledac has, as Microsoft claimed, depressed spam levels.

Microsoft has targeted Waledac before. In April 2009, the company issued a version of its Malicious Software Removal Tool (MSRT) that scrubbed the malware from Waledac-infected Windows PCs. In the second half of last year, MSRT and other Microsoft software, notably the free anti-virus program Microsoft Security Essentials, cleaned 96,000 systems of Waledac, boasted Jeff Williams , the director of Microsoft's Malware Protection Center, today.

Williams, who urged users to run MSRT and keep their anti-virus software up to date, also hinted that Microsoft had more on Waledac than it had disclosed. "We're not done," he said. "Stay tuned."

Robert McMillan, of the IDG News Service, contributed to this report.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is .

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