Facebook says security flaw may have affected 50 mn users, shares down 3%

Facebook Inc has discovered a security flaw affecting about 50 million user accounts which could have allowed attackers to take over the accounts, the social networking company said on Friday.

Facebook has since fixed the vulnerability and informed law enforcement, it said.

Attackers stole Facebook access tokens through its "view as" feature, which they could then use to take over people's accounts. 

"View as" is a feature that allows users to see what their own profile looks like to someone else.

Facebook has reset the access tokens of the 50 million affected accounts, it said. As a precaution, the company