Google first acknowledged the problem around 11 a.m. U.S. Eastern Time, and declared it resolved at 12:40 p.m., saying it had affected "less than" 1.38 percent of the Google Mail user base.

Assuming the outage hit 1.37 percent of Gmail's approximately 350 million active users, then the total number of affected users would have been about 4.79 million.

Users impacted were unable to access their Gmail accounts, according to the .

Earlier this week, an undetermined number of Google Spreadsheets users for about two hours by a bug that displayed frequent CAPTCHA screens when they attempted to open files. CAPTCHA systems ask users to enter text they display in a box before giving them access to specific functionality in an application. The purpose is to make sure that the users are human beings and not machines that may attempt to misuse or abuse the application in question.

Gmail suffered an outage in mid-April that lasted more than one hour and may have impacted more than 33 million users.