How to Make Your Facebook Account Safe
After hearing a lot on privacy issue, Facebook staff underwent huge mind churning and released a new security features which will record the names/details of computers and mobiles used by account holders to log in to their Facebook Account. This feature is available under Account Settings—->Account Security
If the particular account is accessed from any other device an instant email is sent to user. The idea behind this feature is to stop hacking or spamming activities
If a genuine user logs in from some other device he will be asked to answer a security question.
This security check will not be done very often; users will go through this process only when Facebook detects some unusual activity in a particular account.
The big question is how easy it is to maintain such records of user traits and online activities when you are about to reach the mark of 500 million users? If it is going to be done by recording IP addresses, then few internet service providers change IP address of user with every login.
And recording personal traits and monitoring online activities isn’t a breach of privacy again?
Source Facebook Blog




