Microsoft said that the anti-malware tool it pushed 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 centre 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 November 11 to November 19, said Scott Wu, Scott Molenkamp and Hamish O'Dea, MSRT purged more than 994,000 machines of what the tool recognises 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, cyber-crooks can pull in as much as $5 million (£3.3 million) a year by installing the rogue programs on PCs, then tricking 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's infected a system.
The clean-up job was one of Microsoft's biggest ever. In June 2008, MSRT sniffed out 1.2 million PCs infected with a family of password stealers, while in February, it scrubbed the Vundo Trojan from about a million machines. Over several months at the end of last year, the tool hit the then-notorious Storm Trojan hard, eventually eradicating it from a half-million PCs, something Microsoft bragged about later.
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 percent 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 email.
Windows users can download the MSRT manually from Microsoft's website, or via the Windows Update service.