Regina Buenaobra posted on the forums today that there has been a change in the way that email authorization is being handled.
We have recently adjusted the sensitivity of the Guild Wars 2 e-mail authentication system to make it even more secure. One result of this change is that players may be briefly denied access to their account until they approve access from their current network.
If you attempted to sign in to the Guild Wars 2 game client or official website and were denied access, check your email for a notification from us. If you recognize the log-in attempt, follow the link in the email and select Remember this Network on the page.
Security Tips: If you receive an email asking you to approve a login attempt from an unknown network, don’t do it! It could be that someone attempted to log in using your username and password. Instead, change your password viahttps://account.guildwars2.com. Also, be on the lookout for phishing attempts that try to direct you to malicious websites. The official Guild Wars 2 domain is *.guildwars2.com, so check your browser to make sure that you’re in the right place.
For more information on e-mail authentication, see this Knowledge Base article:http://en.support.guildwars2.com/app/answers/detail/a_id/9192
The original post can be found here.