To date, the company has released proof-of-concept exploit code for Sun Directory Server 7.0 and IBM Tivoli Directory Server 6.2. Microsoft's single patch, MS10-001, affects Windows 2000 through Windows 7. Its severity is rated "critical" for Windows 2000 and "low" for other Windows systems.
 
"Due to the memory model in Windows 2000, the vulnerability is critical on that version of the Windows operating system, all others receive a low severity rating," said Qualys CTO Wolfgang Kandek in an e-mailed statement in Bangalore on Wednesday.  "The flaw can be exploited through any OpenType-enabled application such as Internet Explorer, PowerPoint, and Word by viewing a Web page or a document."

Microsoft is recommending that Windows 2000 customers deploy the patch immediately. The company credits Google's Tavis Ormandy with reporting the issue.

Adobe has released an update for a month-old critical vulnerability in Adobe Reader 9.2 and Acrobat 9.2, and Adobe Reader 8.1.7 and Acrobat 8.1.7 for Windows and Macintosh, and Adobe Reader 9.2 for UNIX.

Ben Greenbaum, senior research manager with Symantec Security Response said in an e-mailed statement that this vulnerability is being actively exploited by attackers. "Attack attempts seemed to peak near the end of December and then drop off, but we're continuing to see limited attempts at exploitation, and more reliable exploits could still be developed," he said.