This is new and shows facebook is keeping track of IPs to some degree, although they still probably can't figure out a good automatic method to filter legit from fake. Anyway, I logged into an account from a new IP and was fine then logged out and about an hour later tried to log back in and got a normal "challenge" to verify birthday. This often happens where you can log in fine from a new IP and then for whatever reason, the IP triggers a response on a later login. Anyway, I in addition to the normal birthday challenge, I got this new thing "Step 3" asking me to confirm the earlier login. What's interesting is if you click the "guess" link, it displayed the IP of my earlier login. No big concern, but just shows FB is keeping track of the login IPs and in the future may try to get more aggressive with the info.