Hackers have lists of email addresses and passwords stolen from other games and web sites, and collected through spyware, and are systematically testing Guild Wars 2 looking for matching accounts. To protect yourself, use a strong, unique password for Guild Wars 2 that you've never used anywhere else!
When accounts are hacked and then used for botting or spamming ads for gold sales, we ban the accounts until we can return them to their rightful owner. If you login and see the message, "this account has been permanently banned for a violation of the User Agreement," and if you're not a gold seller, it's likely that your account was hacked. Please contact customer support using the instructions below.
If you see email authentication messages in your inbox asking you to approve a login that you didn't initiate and from someplace you don't recognize, that's a sign that a hacker knows your account name and password, and is only being prevented by the email authentication feature from accessing your account. You should immediately change your password to a new, unique password that you've never used anywhere else.