ArenaNet has announced that any players who have not changed their passwords since September 2012 will be forced to do so next week.

On February 7 any players who haven’t updated their passwords will be forced to change before they can log in to the game. If you haven’t updated you can go to your account management page and change your password there or you can wait until February 7 where you will be prompted to do so before logging in.

This is basically to ensure that all accounts are safe from hackers.