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It has become a familiar pattern: A hacker posts exploit code to a security Web site; Microsoft follows soon after with a warning to customers.

The pattern was repeated again Thursday, only this time Microsoft's warning that it is investigating "new public reports" of a critical bug in Windows comes more than two months after sample code showing how to take advantage of the flaw was posted to the Web. Microsoft's advisory can be found here.

The flaw that Microsoft warned about is in an ActiveX control (called WebViewFolderIcon) used by the Windows' graphical user interface software. It was first disclosed on July 18 as part of a month-long project by hacker HD Moore to expose problems in browser software. Moore's blog post on the flaw can be found here.

Bugs Not Yet Investigated

Moore called his project the "Month of Browser Bugs" and ended up disclosing a total of 22 Microsoft vulnerabilities during the period.

A few days ago, Moore quietly added exploit code for this latest flaw to his Metasploit hacking tool. The exploit caught Microsoft's attention after it was posted to the milw0rm.com Web site, Moore said. But the security researcher believes that any competent hacker could have developed an exploit based on his July blog posting.

So far, Microsoft has patched only two of Moore's flaws. In fact, Microsoft engineers haven't even been able to investigate close to a third of the vulnerabilities, Moore said.

Patches Coming Soon

Microsoft executives could not immediately be reached for comment, but the company's security advisory said this latest WebViewFolderIcon bug will be patched on Oct. 10.

"We have been in contact with HD Moore and at this time our investigations have revealed that most issues relating to Internet Explorer in particular will result in the browser closing unexpectedly," Microsoft's public relations agency said Thursday in a statement. "Because of their nature, most of these issues will more likely be resolved through a service pack release rather than a security update."

Microsoft has been busy this month, rushing out an emergency, "out-of-cycle" fix for a flaw in Internet Explorer's Vector Markup Language rendering engine that was being widely exploited by attackers.

Exploitable Bugs Unreported

Microsoft has even more work ahead of it, according to Moore. In early August, he handed Microsoft another 70 bugs that he had not publicly disclosed.

Still, he believes that more of his flaws should have been fixed by now.

"I was kind of amused that they would do an out-of-cycle patch for the VML bug, but would let all of these lapse," he said.

Microsoft has told him that at least four of his bugs are "exploitable issues," meaning that an attacker could take advantage of them to run unauthorized software on a victim's computer, Moore said.

Microsoft Response Slow

Earlier this week, Symantec said that Microsoft was the slowest of the major browser-makers at patching its bugs during the first half of this year.

But according to Symantec's numbers, Microsoft patched IE bugs, on average, nine days after the public disclosure of a flaw. Most of the 22 Month of Browser Bugs flaws have been in public for two months now.