Facebook is admitting that it "unintentionally" uploaded the email contacts of more than 1.5 million users without asking permission.

The social network claims that all users that fell victim to this glitch would be notified and all the contacts it had grabbed without consent would be deleted. 

Facebook started to take contacts without the consent of new users as of May 2016.  Before this date, they were asked if they wanted to upload their address book voluntarily.  Facebook is believed to have used the data to help map social and personal connections between users.

It's not the first time the company was caught mishandling the data of some of its billions of users.  Last month, Facebook discovered that the passwords of about 600 million users were stored internally in plain text for months.  Last year, it came out that Facebook allowed the political consultancy Cambridge Analytica to gain access to the data of 87 million people.  And it was hit with a fine of about AU$785,000 by the UK's privacy watchdog last year for failing to protect user data.