In the last couple of hours, Facebook has been unstable for many users (including us), according to numerous tweets from those affected. In the last 15 minutes or so, Facebook seems to be completely inaccessible.

While downtime happens far more rarely to Facebook than, say, Twitter, world's largest social network has occasionally had stability issues. It's a big deal: With 500 million active users, complaints about downtime mount up pretty quickly.

We’ve contacted Facebook to see what’s wrong. We’ll keep you updated as we learn more.

Update: Facebook has reached out to us with the following statement: "We are experiencing site issues that are affecting some people. As a result, the site may be slow or time out for some users. We are working to resolve the issue as quickly as possible."

Update #2: Although it's still slow for some, Facebook now seems to be working normally for most users.