What's more, Facebook employees can't get into their offices, because their IDs stopped working as well...
Which sounds like the worst badge system ever created because it should be able to run independently from their network. Turns out, just like the rest of Facebook, it's a dumpster fire.
Actually, I see this as a malfunction of a high security system.
Security systems can malfunction in two ways:
1. Allowing unauthorized access
2. Disallowing authorized access
We usually hear about number 1, which is something that higher levels of security should prevent. However, such higher security makes number 2 more likely to happen, which is the situation that Facebook encountered.
It reminds me of the incident known as apocalpyPS3, when the console's secure clock (which can't be set by the user) read February 29, 2010, which caused the DRM system to think that there was some hacking going on (since that date should be impossible), and then panicked and prevented the users from playing games.for a day, all because of the DRM being overly active and paranoid.