LONDON (AP) — Ireland's privacy regulator says it is investigating Facebook over the social media giant's recent revelation that it had left hundreds of millions of user passwords exposed.

The Irish Data Protection Commission said Thursday that it opened a statutory inquiry this week into Facebook after the company notified it about the security lapse.

The company said last month that it had inadvertently stored passwords for users of Facebook, Facebook Lite and Instagram in plain text, making it possible for employees to search them.

It said the passwords were stored on internal company servers, where no outsiders could access them.

The commission already has 10 other investigations under way into Facebook and its subsidiaries, which also include Whatsapp, over whether it's complying with European privacy rules.