The controversial zombie game The War Z has been taken offline after a major hack stole email addresses and user details - and gamers have been warned to change their passwords.

Data including email addresses, encrypted passwords, IP addresses and in-game character names were stolen from game and forum databases. The game has 600,000 registered users, and a reported 150,000 daily users, battling for survival in a zombie-infested online 'world'. It became the subject of controversy earlier this year after it was pulled from the Steam PC game store for inaccurate descriptions of game content.

“We are investigating whether additional information may have been obtained,” said makers Hammerpoint Studios in a statement.

The company said that while all of the stolen passwords had been encrypted, their research had shown that many of their users were not using strong passwords, and their details could be vulnerable to brute force methods.

“We are asking all of our players to please change your passwords immediately. If you use the same password for accounts on other services, you should change those passwords as well," Hammerpoint said in its statement.

The company said that payments for the game were processed by a third party, so it was unlikely that this information had been stolen.

“We have identified number of ways access was obtained and have enhanced our security to improve game and forum safety.,” Hammerpoint said. “We are undertaking a full review and update of our servers and the services we use and adding additional security mechanisms."ur servers and the services we use and adding additional security mechanisms."

Recent ESET research found that up to 30% of PC gamers disable security features in order to speed up games and prevent lag, potentially leaving themselves open to malicious software infection (read more about ESET gaming/malware research).