Up to 500,000 people may have been affected by the flaw, which allowed hundreds of apps to access data including people's jobs, ages and location information.
The company knew about the issue in March but did not disclose it. There is no suggestion that any credit card or bank information was exposed, but exposing private information about individuals can make them more vulnerable to fraud.
Google+ was launched in 2011, quickly becoming known as a failed attempt to compete with Facebook. However, the consumer version of Google+ currently has low usage and engagement: 90% of Google+ user sessions are less than five seconds.
