Microsoft has rushed out an emergency patch after a regular update to its security tools caused sessions of Google's Chrome browser to be falsely identified as the Zeus trojan.
Following Friday's release of an update adding the trojan's signature to its threat detection tools, users of Microsoft's Security Essentials and Forefront products began tweeting that Chrome was being identified as a Zeus infection.
The security tools recommended that Chrome be removed from users' systems.
The software giant responded quickly to the complaints, and released a further update several hours later which corrected the problem.
"On September 30th, 2011, an incorrect detection for PWS:Win32/Zbot was identified and as a result, Google Chrome was inadvertently blocked and in some cases removed," Microsoft wrote on its web site, explaining the issue.
It also apologised for the error, and recommended customers apply the latest update and reinstall Chrome.
"Affected customers should manually update Microsoft Security Essentials with the latest signatures. After updating the definitions, reinstall Google Chrome. We apologize for the inconvenience this may have caused our customers."
Given that Microsoft operates Internet Explorer, a rival browser to Google's Chrome, some Twitter users were unconvinced that the false identification and removal was really an error.
"Microsoft AV tools marking Chrome as Zbot. Classifying your competition as malware might be taking things too far MS," wrote a user going by the name @bryanbrannigan.
The Zeus trojan is principally used by cyber criminals to steal online banking details, and commonly targets users of Microsoft's Windows operating system.