Facebook chat is now down as the social network races to close a security hole that let people see their friends' live chats. The security bug was exploited, ironically enough, by fiddling one's privacy settings, as this TechCrunch video demonstrates.
So, just to recap: Facebook compromised people's privacy via the very code it wrote to enhance people's privacy. This follows Facebook accidentally misdirecting private messages to the wrong users and accidentally exposing people's private email addresses, all within the past three months. We'd expect an abject apology from the company for accidentally exposing user information so often — if it didn't expose user information on purpose even more frequently.
Update: Facebook is telling the press it has patched the security hole. Chat seems to have returned.