The first images crafted to contain a malicious program that can take control of a PC have been found on the net.
Viewing jpegs could soon be a risky business
Security experts have been expecting such images to turn up after Microsoft revealed a weakness in the way Windows handles the popular Jpeg format.
Soon after this discovery, a program started circulating online that was written to exploit this bug.
The poisoned images were posted to a porn newsgroup at the weekend and were found by Usenet provider Easynews.
Poisoned pictures containing the bug have been widely predicted following the discovery of the Jpeg bug that afflicts more than a dozen Microsoft programs.
To fall victim to the poisoned pictures, users must view it using Windows Explorer.
Once in place, the code then tells an infected machine to contact a server on the web to download another program that lets it be taken over remotely by an attacker.
Windows XP Service Pack 1
Windows Server 2003
Internet Explorer 6 SP1
Office XP SP3
Digital Image Pro 7.0
Digital Image Pro 9
Digital Image Suite 9
Picture It! 2002
Picture It! 7.0
Picture It! 9
Producer for PowerPoint
Project 2002 SP1
Visio 2002 SP2
Visual Studio .NET 2002
Visual Studio .NET 2003
The partner server that held the remote control code has now been shut down.
Oliver Friedrichs, senior manager with Symantec Security Response, said that he expected future versions of the bug to strike when images are viewed with the Internet Explorer browser and Outlook.
Microsoft played down the threat from the images. In a statement it said few people were likely to fall victim because of the series of steps they had to go through to get infected.
The net watchdog, the Internet Storm Center, said the poisoned images only crashed computers in tests, but added that working versions were probably close to being finished.
It also said that poisoned images were starting to circulate on AOL Instant Messenger.
Security firm F-Secure said that, so far, the few poisoned pictures posted on Usenet were not a virus because they do not replicate.
"Unfortunately I have a nasty feeling we might sooner or later see a mass-mailer worm using a Jpeg image as the attachment," wrote Mikko Hypponen in the company's online journal.
Users who have updated their Windows XP machines with the SP2 update could still be at risk from this bug if they are running unpatched programs, such as Microsoft Office, that are vulnerable.
Microsoft is urging people to update their version of Windows and download patches to close the loophole.
Some security firms have also produced tools that let users scan computers to see which machines are vulnerable to the exploit.
Anti-virus firms have updated their software to recognise the signature of the virus-bearing images.