Widespread Worm May Be Building A New Botnet

A rapidly spreading worm infection may be a tool for building out a major new botnet, according to security researchers who have been watching the aggressive Confickr/Downadup worm multiply around the globe. The number of PCs infected by the worm has now reached 8.9 million, according to the latest count by F-Secure, while other researchers say it's closer to half a million or so.

Either way, security experts are anxiously awaiting the attackers' next move. They suspect a massive botnet is in the works, but so far the attackers haven't completely tipped their hand. The mere infection of so many machines that could then be controlled by a third party indicates it is indeed a botnet-in-progress, according to Damballa. "It's a close call. If it has the potential for a remote, malicious third party to do whatever they want, that makes it a botnet," says Paul Royal, chief scientist for the antibotnet company.

The code automatically generates domains that infected machines connect to, which could lay the groundwork for a botnet command and control infrastructure. But so far, there's been no official botnet activity. "The infected machines are looking at 250 different domains a day to try and download additional code, but so far all those domains we've looked at have either been unregistered, accidental random variations that happen to point to an existing site, registrars with a wildcard DNS for unregistered domains, or other researchers trying to get a count of the bots," says Joe Stewart, director of malware research for SecureWorks. And the fact that domains aren't actually set up means it's not yet ready as a botnet, he says.

"Whoever is behind this is not ready to deploy his or her code just yet. Maybe they first need to figure out how to get their botnet controller to scale to handle [millions of] nodes," Stewart notes.

One thing that is certain: The worm is spreading like wildfire, and its creators appear to be trying to beat the clock and infect as many machines as they can that haven't yet patched for the Windows vulnerability that it exploits on Windows 2000, XP, and Windows Server 2003 systems. The perpetrators have been cranking out new variants of the worm to evade detection, and, so far, its main mission has been pushing rogue antivirus software.

"Its primary [function] is to shill rogue AV software," says Damballa's Royal, who first spotted major spikes in the worm around Thanksgiving, when it was in excess of 500,000 IPs.

This is not your father's worm, however. Confickr/Downadup spreads fast like a Slammer, but this one has a command and control channel: "It propagates like a worm and can act like a bot. Perhaps it's representative of a hybrid that may represent a new class of malware" rather than the social networking or email lures of old, he says.

According to Damballa's latest data, most of the infected machines are in the U.S., followed by South America. And according to Royal, Damballa today spotted nearly 76,000 infected machines trying to connect to Confickr domains in just five minutes.

Microsoft says the victims mainly have been those who had not yet patched for the vulnerability when the worm was unleashed. "Most of these customers are running large networks as file sharing and network shares are more common in those environments than in homes. This malware has infected computers in many different parts of the world," according to a Microsoft researcher blog post .

The software giant has been warning users to patch for the flaw, and as of yesterday had updated its Malicious Software Removal Tool to scan for the exploit. So why so many infected machines for a known vulnerability that dates back to last fall? The worm actually prevents an already-infected machine from getting cleaned up: "The worm blocks access to Microsoft's Websites and disables the automatic update functionality. That prevents any infected computer from downloading MSRT and getting to the exploit fix -- if not installed already," says Patrik Runald, chief security advisor at F-Secure. "It also blocks access to security vendors Websites and update services, meaning that any antivirus software is unable to update. Therefore, it will take quite some time to clean up all infected computers."

"So far, it's just spreading, but it wouldn't surprise me if they turn it into a botnet that can later be used to send spam, steal information, etc.," F-Secure's Runald says.

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