Millions of account details for World of Warcraft, StarCraft and Diablo players have been stolen in an attack on the maker Blizzard.
Blizzard announced details of the breach in a message posted to its Battle.net account management service.
Players in North America are being advised by Blizzard to change their login details for the account management service.
Blizzard claimed that there is no evidence at this stage to suggest that credit card numbers and other personal details had been stolen.
Blizzard boss Mike Morhaime said the company discovered on August 4th that there had been 'unauthorised and illegal access' to its internal network.
The investigations into the attack have so far revealed that whoever broke in got a copy of a list of all email addresses for users outside China.
Gamers who play World of Warcraft, StarCraft 2 and Diablo 3 use Battle.net as to log in and manage their account.
Also accessed was information about the security questions and account authenticators used by players on North American servers.
This includes players in Latin America, Australia, New Zealand and Southeast Asia, in addition to those found in the US and Canada.
The hackers also stole a crytographically scrambled list of the passwords used on North American Battle.net accounts.
Mr Morhaime said the technique used to hide these words makes it hard to unscramble them.
As a result, Blizzard do not believe that the hackers will be able to access people's Battle.net accounts. However, players on the North America service are still being encouraged to change their passwords.
Blizzard has already implemented steps that force Battle.net users to change their secret questions.
The company stated that it has found 'no evidence' that credit card numbers, billing addresses or real names had been exposed.
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