In a statement, Mike Reavey, director of the Microsoft Security Response Center, provided few particulars other than saying the two bulletins -- one affecting Visual Studio and one affecting Internet Explorer -- will address a single, overall issue. "While we can't go into specifics about the issue prior to release, we can say that the Visual Studio bulletin will address an issue that can affect certain types of applications," he said. "The Internet Explorer bulletin will provide defense-in-depth changes to Internet Explorer to help provide additional protections for the issues addressed by the Visual Studio bulletin."
He said that the Internet Explorer bulletin will address "critical" issues in Internet Explorer unrelated to the Visual Studio vulnerability.
He also said that Microsoft customers who have the most current security updates are protected from known attacks related to the vulnerabilities addressed by the two emergency bulletins.
A substantial portion of Microsoft customers are nonetheless likely to have vulnerable software. In mid-2008, according to Google, 45.2% of Internet users visiting the search site weren't using the most up-to-date version of their browser.
Out-of-band patches are unusual but certainly not unheard of. Last December, Microsoft released an out-of-band security update, MS08-078, to fix a vulnerability in Internet Explorer.
The company also released an out-of-band update last October, MS08-067, to fix a problem with Windows Server that could, and did, allow a malicious worm to spread: The vulnerability was subsequently exploited by the Conficker/Downadup worm because Microsoft users didn't patch quickly enough.
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