More than 11,000 Guild Wars 2 accounts were accessed by parties other than their owners over the weekend, ArenaNet has announced.
Access was achieved by trying username and password combinations stolen from compromised unofficial Guild Wars 2 fan sites, the developer said.
"If you don't want your account hacked, don't use the same email address and password for Guild Wars 2 that you've used for another game or web site," said ArenaNet.
"Hackers have big lists of email addresses and passwords that they've harvested from malware and from security vulnerabilities in other games and web sites, and they're systematically testing Guild Wars 2 looking for matching accounts."
As a precaution, the developer has begun emailing customers when an account is accessed from a new location.
Anecdotal reports suggest many of the account access attempts originate in China.