This stark message comes after thousands have submitted tickets after accounts had been tampered with. The studio talks of "big lists" hackers keep of "harvested" account details from malware.
The team allege that hacking groups are "systematically testing" Guild Wars 2 for matching email and password combinations that they've trawled from spyware.
"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," they warned on the official wikia. "To protect yourself, use a strong, unique password for Guild Wars 2 that you've never used anywhere else!"
"If your current password isn't unique to Guild Wars 2, change it today! Do not under any circumstances use the same password for Guild Wars 2 as you do for your email account."
"We've observed hack attempts against hundreds of thousands of accounts that don't even exist. To protect those people in case they purchase Guild Wars 2 and create an account, we will now disallow customers from picking passwords that we've previously seen used in a hack attempt." The ArenaNet F2P MMO has been plagued by hackers.
A report from GamesIndustry.biz reveals that 11,074 support requests have been raised with ArenaNet over password related matters. A Guild Wars 2 fan site has also reportedly been hacked.