Mark would have written this post himself, but is busy helping out with everything going on right now, so I've been asked to explain why we're launching this expansion.

You've heard it before, and you'll hear it again; here at Facebook, we want to help people understand their world. We started at one school, and realized over and over again that this site was useful to everyone—not just to Harvard students, not just to college students, not just to students, not just to former students. We've kept growing to accommodate this fact.

This includes your friends who graduated pre-Facebook (yes, there was such a time), your friends who don't have school or work email addresses, and your friends whose schools don't give out email addresses. Now you can all connect.

This doesn't mean that anyone can see your profile, however. Your profile is just as closed off as it ever was. Our network structure is not going away. College and work networks still require an authenticated email address to join. Only people in your networks and confirmed friends can see your profile.

We listened to what you guys had to say and built extra privacy controls that we launched last week. If you're uncomfortable with regional users being able to see you on Facebook, you can always change your privacy settings to prevent people from finding you in searches and communicating with you. Also, we've built out a bunch of tools that will help verify new users and prevent spammers from bothering you. You can read about these tools here.

Facebook is still yours, for you and your friends (all of your friends) to connect with each other and share information.

Carolyn, Facebook's resident blogger, is expecting instant notoriety and perhaps a few Facebook groups to arise from this post.