Users of Google's Chrome browser are in an uproar after antivirus software from Microsoft classified it as virulent piece of malware that should be deleted immediately.

On Friday, a faulty signature update for both Microsoft Security Essentials and Microsoft Forefront incorrectly detected the Chrome executable file for Windows as a component of the notorious ZeuS trojan, one of the better-known pieces of malware used to steal victims' bank account credentials. Microsoft fixed the problem a few hours later, but by then the false positive had left huge numbers of Chrome users without bookmarks and browser plugins they rely on to access commonly used webpages and services.

“Worst impact has been for people who are long-time chrome users, as all of their bookmarks and sessions are configured in chrome,” one affected Reg reader wrote in an email. "Most annoying is the required reboot which causes productivity loss, esp for people who run VMs and such on their desktop as it can take a while to get everything back up and going.”

The reader, who asked not to be named because his employer forbids him from speaking to the press, said Chrome's beta version is unaffected, making it a suitable substitute until Microsoft can correct the error. A separate Chrome user said in this support forum that “Chrome users that do not send usage statistics to Google are unaffected.”

It was impossible to immediately verify those claims. A Google spokesman declined to confirm or provide any details, and a Microsoft statement also omitted details. A Microsoft advisory here reported that an “incorrect detection for PWS:Win32/Zbot” has been identified, but made no reference of Chrome. Zbot is another name used to identify ZeuS.

According to other people participating in the Chrome support forum, the false positive is causing plenty of teeth-gnashing in IT departments.

“Pleasepleaseplease someone come up with a solution to this!” a user with the alias maganam wrote. “The tech department in my office is stumped and I'm going crazy trying to work on Firefox!”

After this article was first published, a Microsoft spokeswoman released a statement that read in part: "We have already fixed the issue -- we released an updated signature (1.113.672.0) at 9:57 a.m. PDT -- but approximately 3,000 customers were impacted. Affected customers should manually update Microsoft Security Essentials (MSE) with the latest signatures. To do this, simply launch MSE, go to the update tab and click the Update button, and then reinstall Google Chrome. We apologize for the inconvenience this may have caused our customers."

Google said in a blog post published several hours after this article was first posted that it planned to release an update that will automatically repair damaged installations of Chrome in the next day. The post also included steps affected users can take to manually fix their browser. ®

This article was updated to include comment from Microsoft and add information contained in Google's blog post.