Google's Chrome web browser has made significantly usage inroads in the past year, and some are predicting that it could actually surpass usage in Mozilla's Firefox browser by the beginning of 2012. But not if Microsoft can help it: The software giant's free antivirus solution, Security Essentials, was flagging Chrome as malware and even deleting it from users' PCs late last week. It was like an early Christmas present for Mozilla.

OK, it's not that dramatic. But Microsoft Security Essentials did inadvertently, if briefly, flag Google Chrome as a Zeus Trojan variant called PWS:Win32/Zbot. And the default action was to automatically block access to the application and, after a scan, delete it.

"On September 30, 2011, an incorrect detection for PWS:Win32/Zbot was identified and as a result, Google Chrome was inadvertently blocked and in some cases removed," a Microsoft statement confirms. "Within a few hours, Microsoft released an update that addresses the issue. Signature versions 1.113.672.0 and higher include this update ... After updating the definitions, reinstall Google Chrome. We apologize for the inconvenience this may have caused our customers."

Microsoft notes that PWS:Win32/Zbot is a password-stealing trojan that monitors for visits to certain websites. Chrome, meanwhile, is a web browser that competes with Microsoft's still-dominate Internet Explorer (IE) web browser. So you can see how the two would be easily confused by modern AV software.

As for the latest browser-usage share numbers, Net Applications shows IE with a commanding overall lead of 54.4 percent usage share, though that's down again from last month's 55.31 percent. Chrome is up a similar amount, to 16.2 percent usage share, and Firefox is holding steady at around 22.5 percent. So while it's unclear why Chrome is expected to catch up to Firefox quickly, one possible outcome is that Chrome and Firefox settle in the same basic 20 to 25 percent range with Microsoft sopping up most of the remainder. We'll see.