Google released a new version of Chrome last month (Chrome 12.0). Microsoft Security Essentials reported the Chrome browser as malware and deleted it from 3,000 computers on Friday. Microsoft apologized for the problem and updated its virus definition file to correct the false-positive problem, according to a post from Ryan Naraine at ZDNet.
Microsoft had this statement for the mistake
Information about incorrect detection of Google Chrome as PWS:Win32/Zbot
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. Within a few hours, Microsoft released an update that addresses the issue. Signature versions 1.113.672.0 and higher include this update. 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.
To get the latest definitions, simply launch Microsoft Security Essentials, go to the update tab and click the Update button. The definitions can be updated manually by visiting the following Microsoft Knowledge Base article:
PWS:Win32/Zbot is a password-stealing trojan that monitors for visits to certain websites. It allows limited backdoor access and control and may terminate certain security-related processes.”