updated 2/15/2012 7:47:27 PM ET 2012-02-16T00:47:27

If you're using Internet Explorer to browse the Web and wondering why you can't access Google, there's a reason — your computer might think it's harboring malware.

Two of Microsoft's anti-virus programs, Microsoft Security Essentials and its business-market sibling Microsoft Forefront, have been mistakenly flagging as malicious, leaving millions of customers unable to get to the world's most visited website, researcher Brian Krebs reported.

( is a joint venture of Microsoft and NBCUniversal.)

This isn't the first time Microsoft has locked horns with Google by accident. Last September, the software titan's anti-virus programs not only marked Google's Chrome browser as malware, but actually removed it automatically from about 3,000 Windows machines.

This accidental Google blacklist stems from this month's "Patch Tuesday," in which Microsoft released updated versions of Forefront and Security Essentials. Both programs issued a false positive alert for, detecting it as infected with the Blackhole Exploit Kit, a piece of malware that enables cybercriminals and other miscreants to build their own botnet.

"My malware inspection updated to 1.119.1972.0 and within 5 minutes started blocking because of JS/Blacole.BW," wrote user "minerat" on Microsoft's TechNet blog. "I'm almost sure this is a false positive given how quiet the rest of the Net is about it. Is anyone else encountering the same thing?"

Another commenter, "Hammeredge," copied the false positive message, which read, "This program is dangerous and exploits the computer on which it is run."

"On February 14, 2012, an incorrect detection for Exploit:JS/Blacole.BW was released," Microsoft said in a statement given to SecurityNewsDaily. "We provided an update to addresses the issue (signature versions 1.119.1988.0 and higher) on the same day. We apologize for the confusion this may have caused our customers."

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