A dodgy spam definition update from Cloudmark has crashed users' email clients.

Users of the anti-spam service were left unable to run either Outlook or Outlook Express without their email clients crashing. Cloudmark blamed the problem on a corrupted file that formed part of the update, issued on Thursday. The firm has now resolved the problem. Users need to install a new version of Cloudmark Desktop, as explained here.

Reg reader Ian was among those hit by the glitch. "I spent 12 hours trying to get our email back up here. The problem appeared on two machines - an exception and closing of Outlook, and the scary warning about ntdll.dll.

"To be honest Cloudmark is a fit and forget product and works really well for us but I was a tad annoyed when I had to hunt on their web site for a message putting their hands up," he added.

Ian was far from alone is suffering problems as posts to Cloudmark's forum's demonstrate.

False positives are well known as something of an Achilles heel for signature-based malware detection. Problems crop up regularly. Cloudmark's whoopsie this week show that signature updates for spam scanners can cause similar problems, occasionally. ®

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