Microsoft has taken aim at a rogue antivirus program called Internet Antivirus Pro.

The company's latest update to its Windows Malicious Software Removal Tool, (MSRT) released Tuesday, adds detection for this dubious program, which masquerades as security software.

Like all of these rogue antivirus products, Internet Antivirus Pro tries to trick victims into installing the software.

It pops up a fake warning message and then pretends to scan the victim's computer. But instead of scanning for malicious software, Internet Antivirus downloads password-stealing software that looks for FTP user names and passwords, presumably so that its creators can install their software on Web servers.

Internet Antivirus installs a browser component that displays fake messages, and it also pops up a fake Windows Security Center, Microsoft said in a blog posting Tuesday.

The software has also used the names General Antivirus and Personal Antivirus.

Rogue antivirus software has been on the rise over the past year and was among the most-detected unwanted software on Windows PCs during the second half of last year, Microsoft said in its recent Security Intelligence Report.

Two rogue Trojans, Renos and Zlob, were found on more than 8 million infected machines, Microsoft said. They use similar techniques to get installed on victims PCs.

Internet Antivirus has been around since the middle of 2008, but it became much more of a problem, starting in mid-April, according to Ben Greenbaum, a senior research manager with Symantec.

"It looks like there was a big push," he said. "Either they've started selling it to other groups, or the original authors are making a much larger attempt to get this on people's machines."

This isn't the first time Microsoft has gone after a rogue antivirus program. Last month it issued detection for a program called Winwebsec.

In November, it added FakeSecSen.

Microsoft updated the MSRT as part of its monthly set of security updates.

This month's set of patches was a whopper, with critical updates for Windows, Internet Explorer and Office. In all, the updates fix 31 vulnerabilities.