Game publisher Ubisoft has fallen victim to a website hack, which exposed data including email addresses, user names and encrypted passwords for users of its online gaming service.

The gaming giant revealed the breach in an email sent out to users of its Uplay online gaming service last night. It remains unclear how many users are affected, or how the stolen passwords were encrypted. Ubisoft sent Uplay users a link to reset their passwords.  The game publisher - whose upcoming title Watch Dogs, pictured, is set in a world ruled by computer hackers - requires gamers to log in using Uplay on popular titles such as its hit Assassin's Creed games.

The email said, “We recently found that one of our Web sites was exploited to gain unauthorised access to some of our online systems. We instantly took steps to close off this access, investigate the incident and begin restoring the integrity of any compromised systems.”

“During this process, we learned that data had been illegally accessed from our account database, including user names, email addresses and encrypted passwords. Please note that no personal payment information is stored with Ubisoft, meaning your debit/credit card information was safe from this intrusion.”

Uplay works across platforms such as PC, Xbox 360, iOS and Facebook. The Uplay system requires users to log in with an email or password, and offers digital extras such as screensavers for PC games, but also works as a Digital Rights Management system (DRM) to prevent copying.

Some gamers responded angrily to the breach - Ubisoft’s Uplay system is compulsory on many games, which has meant that gamers felt strong-armed into handing over data.

One gamer on Ubisoft’s official forums said, “Only reason I have to have this Uplay account is for some Uplay enabled Xbox 360 games. Which forced me to make an account to play. For future reference, I will never buy nor play another Uplay enabled Ubisoft game on Xbox that requires me to make another account on here. You had one job, keep my account information safe!”