Microsoft told users to update Security Essentials with the new definition file, then reinstall Chrome.

For its part, Google slapped a red warning banner at the top of its Google support pages that read, "Alert: Google Chrome has been incorrectly marked as malware by Microsoft security software."

Chrome was fingered as Zbot, better known as Zeus, a widespread botnet Trojan that focuses on stealing online banking credentials, which criminals then use to vacuum money from accounts.

Microsoft isn't the only security software maker to have screwed up in this way: All three of the world's largest antivirus companies -- Symantec, McAfee and Trend Micro -- have issued defective definitions in the past. In some cases, those mistakes have wreaked much more havoc.

In April 2010, for example, a an unknown number of corporate PCs worldwide when it quarantined a crucial Windows XP system file.