Google exposed the private data of hundreds of thousands of users of the Google+ social network and then opted not to disclose the issue this past spring, in part because of fears that doing so would draw regulatory scrutiny and cause reputational damage, according to people briefed on the incident and documents reviewed by The Wall Street Journal.

As part of its response to the incident, the Alphabet Inc. unit on Monday announced a sweeping set of data privacy measures that include permanently shutting down all consumer...