This bug allowed apps that had access to Profile fields that were shared with the user but not marked as public. No developer exploited the vulnerability or misused data, the company's review found.
Although the bug was discovered many months ago, Google didn't disclose it right away.
The Wall Street Journal broke the news of the software bug, reporting that Google chose to not disclose the problem "because of fears that doing so would draw regulatory scrutiny and cause reputational damage".
Google's attempt at a social network was never particularly popular - and became even less so when it admitted that 500,000 users may have had their data exposed.
Google+ API's log data is only for kept two weeks, so it can not confirm which users were impacted by this bug.
"We made Google+ with privacy in mind and therefore keep this API's log data for only two weeks", according to Smith.
The security flaw existed for three years. Users have to provide "explicit permission" in order for them to gain access to it.
Google reveals on a support page that the Google+ app can't be deleted on some Android devices, but they can be disabled on all Android devices.
"Going forward, consumers will get more fine-grained control over what account data they choose to share with each app", Google said.
Such apps include email clients, backup and productivity services, Smith said. To make sure something like this Google+ leak doesn't happen again, this new initiative is set out to protect user's privacy and limit the amount of data developers have access to across the web and Android.
The closure isn't because people are happier using Facebook and Twitter instead of Google's service.
Google will continue to operate Google+ as an enterprise product for companies.
Google+ will be shutting down over a period of about 10 months, and will vanish by next August. Whether the termination announcement today is truly the result of the security issue or the press around it, or reflects a business decision that was merely accelerated by the disclosure, is the subject of much speculation. In addition, Google Account permissions dialog boxes will be split to show each requested permission, one at a time, within its own dialog box.