SAN FRANCISCO — Facebook has inadvertently exposed six million users’ phone numbers and e-mail addresses to unauthorized viewers over the last year, the company said late Friday.

Facebook blamed the data leaks, which began in 2012, on a technical flaw in its huge archive of contact information collected from its 1.1 billion users worldwide. As a result of the problem, Facebook users who downloaded contact data for their list of friends obtained additional information that they were not supposed to have.

Facebook’s security team was alerted to the problem last week and fixed it within 24 hours. But Facebook did not publicly acknowledge the flaw until Friday afternoon, when it published a message on its blog explaining the situation.

A Facebook spokesman said the delay was because of a company procedure stipulating that regulators and affected users be notified before making a public announcement.