Answer: Quite possibly because Facebook’s already forced you to log out and back into your account today

The news: Facebook said hackers exploited a software flaw to access the records of almost 50 million customers. The firm said it had fixed the vulnerability and reported the breach to law enforcement.

The hack: The company said that the hackers had exploited a coding glitch that affected the service’s “View As” feature, which lets people see what their own profile looks like when someone else takes a look at it online. This allowed them to get hold of digital “tokens,” which are software keys that let people access their account without having to log back in every time.

Those keys let the hackers unlock access to people’s accounts. It’s not clear yet what damage they did.

The fix: The firm says it has fixed the flaw and reset the access tokens of almost 50 million accounts. So if you were unexpectedly booted out of your Facebook account today and had to log back in, the chances are you were a victim of the breach. But not necessarily: Facebook also reset the tokens of another 40 million customers as a precautionary measure because their profiles had been viewed using the View As approach over the past 12 months.

Questions, questions—and more questions: Although Facebook appears to have moved swiftly to publicize the breach—it says it only discovered it on Tuesday—there are lots of questions it needs to answer. How long had the hackers been inside Facebook’s network? What exactly did they do with their access? Why, at a time when Facebook is under intense scrutiny over the abuse of its platform to spread fake news, did it not have a tighter grip on the basic security of its system? And did the recent departure of security head Alex Stamos and the move to break up the dedicated security team and distribute people into other departments cause the company to miss the security hole?

This latest disaster adds to a no good, very bad year for the social network, which has also been under intense scrutiny for its failure to protect customer data in the Cambridge Analytica affair.

CEO Mark Zuckerberg and other senior executives have become regulars at congressional hearings to investigate Facebook’s failings. They may soon find themselves hauled back to Washington, DC, once again.