Account security is a huge thing to ArenaNet, and it’s because of this that there is a mandatory password update coming starting February 7th, 2013.
How they plan to do this is to create a blacklist of passwords that have been used by hackers in the past to scan for accounts. This has so far been great for protecting newly created accounts, and due to this they’re asking all customers to change their passwords. So if you haven’t changed it in the past few months you will be asked to do so.
Of course there’s no advantage in waiting until the change is forced from the 7th, and you can chance it by going to your account management site today. You can find out more information on the password change from the Guild Wars 2 blog post.