The security hole could be exploited by hackers or a future internet worm.

Microsoft is recommending that customers patch their computers against the security vulnerability immediately. “JPEG images are commonly used for graphics on websites and digital photographs so this vulnerability is extremely serious,” said Graham Cluley, senior technology consultant for Sophos. “The message, however, is not to panic but to calmly patch your computers now before a virus writer or hacker tries to exploit the loophole and attack innocent users’ computers.”

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A technical bulletin at www.microsoft.com/technet/security/bulletin/MS04-028.mspx describes the latest security problem in detail and includes links to patches supplied by Microsoft.

Sophos warns users of Microsoft Windows XP Service Pack 2 that they may still be at risk from the flaw, even though Microsoft has declared the operating system itself does not require an update, as the vulnerability affects programs as well as the operating system.

“Although the Windows XP SP2 operating system is not reported as having the vulnerability, if you are running programs on XP SP2 which contain the flaw – such as Microsoft Office – you could be putting your computer data in danger. It’s important that everyone at risk ensures their PC is running the latest security updates,” said Cluley.