Facebook Discovers Security Breach Affecting 50 Million Accounts

Facebook has reported a security issue affecting 50 million accounts, leading to a 2.7% drop in its stock. The company has reset access tokens for the affected accounts and informed law enforcement. Additionally, Facebook has temporarily disabled the viewers feature as a precautionary measure.

What was the reaction of Facebook's stock following the news?

What feature is Facebook temporarily turning off in response to the security issue?