A malfunctioning log-in system affected millions of people's ability to access a variety of Google applications on Wednesday, including Gmail and Drive.
The problem, which lasted for about three hours on Wednesday morning, occurred when the main user-authentication system for Google applications was misconfigured.
The improper configuration, introduced on Tuesday, caused log-in requests to be funneled to a small number of servers, which in turn ran out of capacity, and the overload caused them to malfunction.
"At the peak of the outage, this issue affected 50 percent of the Admin panel and 60 percent of Google Sync login requests. The percentages of affected users for other services were lower such as 0.18% users for Gmail," reads an incident report Google posted on Friday.
Google fixed the configuration problem and will take other steps to help prevent the issue from affecting its systems again, including improving monitoring and alerts for server overloads caused by authentication-system misconfiguration. Google also plans to alter the log-in retry behavior of large systems like Gmail, so that they don't aggravate outages caused by server overloads.