Hackers target Microsoft's JPEG flaw.

In a harbinger of security threats to come, hackers have exploited a newly announced flaw in Microsoft Corp. programs and begun circulating malicious code hidden in images that use the popular JPEG format. Software tools to create the malicious images began appearing last month, and this week security experts saw images employing them posted on adult-oriented Usenet newsgroups.

To get the malicious code, a visitor must download the image and view it using Microsoft's Windows Explorer software, said Symantec.

The computer then contacts a server to obtain code that would let an attacker take over the machine remotely.

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While the current exploit is limited future attempts to create malicious images would work on the more popular Outlook and Internet Explorer programs.

The Internet Storm Center at the SANS Institute said an image it found, disclosed on the BugTraq security mailing list, only caused computers to crash in tests, but "we suspect that a working exploit is very close to widespread availability."

Computers with updated versions of anti-virus software should be protected, according to SANS center. Microsoft also has a software patch to fix the flaw and said users who have the Service Pack 2 security update for Windows XP are not affected.

Microsoft disclosed the flaw in question on Sept. 14. It affects people running Windows XP, Windows Server 2003 and later versions of Office.

People who have earlier versions of Windows or Office may also be affected if they are running some specialized applications, such as Digital Image Pro and Visio 2002. The flaw is in a technology that is used to render JPEG images.

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