Microsoft Corp. said that the anti-malware tool it pushes to Windows users as part of Patch Tuesday removed fake security software from nearly a million PCs during nine days this month.
In a post to the company’s malware protection center blog on Wednesday, three of Microsoft’s security researchers spelled out the impact this month’s edition of the Malicious Software Removal Tool (MSRT) has had on phony security software.
In the period from Nov. 11 to 19, according to Scott Wu, Scott Molenkamp and Hamish O’Dea, MSRT purged more than 994,000 machines of what the tool recognizes as “W32/FakeSecSen,” the malware label for a broad range of bogus security program with names such as “Advanced Antivirus,” “Spyware Preventer,” “Ultimate Antivirus 2008” and “XPert Antivirus.”
Windows users have been plagued with a flood of worthless security software in recent months as criminals have discovered that they’re money-makers. According to one researcher, cybercrooks can pull in as much as $5 million per year by installing the rogue programs on PCs, then dunning users with made-up claims that the machine is infected.
Unless consumers fork over a payment — usually $40 to $50 — the constant stream of pop-up messages continue, making the machine hard to use.
Windows users may install the fake programs because they’ve been duped into thinking that they’re real — at times, bogus security software has been ranked high in Internet search results — although the rogue applications are also often secretly installed by malware that has infected a system.
The cleanup job was one of Microsoft’s biggest ever.
In June of this year, MSRT sniffed out 1.2 million PCs infected with a family of password stealers, while in February, it scrubbed the Vundo Trojan horse from about a million machines.
Over several months at the end of last year, the tool hit the then-notorious Storm Trojan horse hard, eventually eradicating it from a half-million PCs.
Microsoft bragged about later, pointing out that the malware search-and-destroy tool it distributes to Windows users disinfected so many bots that the hackers threw in the towel.
“They realized they were in our gun sights,” said Jimmy Kuo, a principal architect with Microsoft’s malware protection center, the group responsible for the Malicious Software Removal Tool (MSRT).
Microsoft updates and automatically redistributes the software tool to Windows users each month on Patch Tuesday.
Kuo had noted that last year the criminals behind the Storm Trojan – malware designed to compromise PCs and add them to a botnet, or collection of infected machines – tried to keep pace with Microsoft and the MSRT.
“They were anticipating our monthly release [of MSRT],” said Kuo, “with new versions that were ready to go immediately before our release.”
The bunch controlling the Storm botnet knew that it took Kuo’s group several days to create new definitions for the MSRT, and that Microsoft held to a once-a-month release schedule for the tool. And they used that lag time and set schedule to their advantage.
“They knew that it takes [us] a week or more to create new definitions, and they were prepared to update their botnet immediately prior to MSRT releasing,” he said, adding that the hackers would get a new version of the Trojan on to already-infected members of the Storm botnet to try to hold on to the machines after Windows had downloaded the newest version of the MSRT.
The idea was to preempt detection by swapping out the Storm bot already on the PC with a version less likely to be identified by the MSRT.
It didn’t work, said Kuo. “They found out that even that was a losing battle,” he said. “Even though they were able to maintain parts of their botnet, they knew they were in our gun sights. And ultimately they gave up.”
According to Kuo, it was the hammering Microsoft gave the Storm botnet that sent the hackers packing.
In the last four months of 2007, the MSRT disinfected more than 526,000 PCs plagued by the Storm bot, he claimed. The bulk of those — more than 291,000 — were cleaned in September, when Microsoft first added Storm detection to the MSRT.
In October, the number dipped to around 90,000, then bounced back to about 100,000 each month in November and December. The front-loaded numbers, said Kuo, were typical, since the first month that the MSRT has a new malware definition, the tool cleanses all machines that have ever been infected. In the following months, it can only disinfect PCs that have been infected since the last release of the tool.
Storm, which first appeared in early 2007 – and got the moniker because it was first disseminated in spam messages that claimed to have news of a massive series of winter storms that swept Europe — has been linked to the Russian Business Network (RBN), a shadowy network of malware and hacker hosting services once based in St. Petersburg.
But while earlier this year, Kuo was happy to take the credit on behalf of Microsoft for shrinking Storm, he was realistic about the overall impact. “What we did was to drive them [the Storm bot herders] elsewhere,” he said. “They’re probably out there still making money with some other botnet.”
This time, Microsoft took the opportunity to pat itself on the back again. Although each FakeSecSen installation normally contains an .exe file, one or two .dat files, a control panel applet and other components, the MSRT found that only about 20 per cent of the infected PCs it uncovered still harboured the .exe.
(Other components remained, however, as evidence of the bogus program’s installation).
Microsoft speculated that the .exe files had been removed by other anti-malware software that had overlooked the other pieces. “Microsoft was able to thoroughly clean systems of FakeSecSen while other malware-detection tools may not have caught and cleaned as many executables,” said Bill Sisk, a Microsoft security spokesman, in an e-mail.
Windows users can download the MSRT manually from Microsoft’s Web site or via the Windows Update service.