For those players who set their password prior to the introduction of password blacklist checking on September 12, 2012.
As part of ArenaNet's ongoing battle against Guild Wars 2 account hacking, all players who created a password prior to the introduction of password blacklist checking on September 12, 2012, will be required to enter a new password.
"Account security is a very important topic for us" wrote Guild Wars 2 head of community Martin Kerstein.
"One of the ways we protect your account is by creating a blacklist of passwords that have been used in the past by hackers to scan for accounts. As this blacklist has been very successful for protecting newly created accounts, we have asked all our existing customers to change their passwords.
"In fact, for those customers with passwords chosen before the introduction of blacklisting, we have displayed a red banner in the launcher for the past three months, encouraging (but not requiring) a password change. Starting on February 7, 2013, we will change it to a requirement.
"Thus, if you are still using a password that was chosen before the introduction of password blacklisting on September 12, 2012, you will need to choose a new password."
There's no need to wait until February 7 – if you are using an old password then visit the account management website to change it today.