Guild Wars 2 has been out for just over a day (officially, anyway) and accounts are already falling to the unscrupulous. We're talking about hacking, of course, and all other illegal account shenanigans, which actually began before launch, if you'd believe that.
A fair chunk of the community has reported and is reporting unauthorized attempts to access their accounts, typically by means of password resets. Enough so to raise serious concerns, at least.
If you receive an email requesting a password change that you did not personally authorize, ArenaNet suggests simply ignoring said email. Do nothing, basically. As for phishing attempts, do not reply to these. Keep in mind Anet staff will never ask for your password.
For the extra cautious, consider using a totally new email for your Guild Wars account, and don't repeat passwords. Be smart about your login credentials. And if you're World of Warcraft account was previously hacked, definitely avoid using the same email and password combo for Guild Wars 2 -- or anything else, for that matter.
Regardless, Guild Wars 2 is off to a strong start. Prior to launch, Headstart access saw a record-breaking 400,000 concurrent players, with over one million pre-purchases.