By Carlo Versano

Facebook shares dropped Friday afternoon after the company announced that 50 million accounts may have been compromised by hackers exploiting a security vulnerability.

Guy Rosen, the company's VP of product management, said the breach was discovered on Tuesday and affected its "View As" feature, which allows people to see what their own profile looks like to someone else. Rosen said the vulnerability has been patched.

"We’re taking this incredibly seriously and wanted to let everyone know what’s happened and the immediate action we’ve taken to protect people’s security," Rosen, wrote in a blog post on Friday.

Facebook ($FB) discovered that unknown attackers manipulated a piece of code that allowed them to steal security tokens that usually keep accounts logged in.

The post was light on detail and was seemingly intended to show the company's efforts at transparency, just months after it was pilloried for a mishandling of the Cambridge Analytica breach.

After that scandal, CEO Mark Zuckerberg said in a Facebook post, "We have a responsibility to protect your data, and if we can't, then we don't deserve to serve you."