Ubisoft has been hacked with usernames, email addresses and encrypted passwords compromised.
The French video game publisher said payment information was not compromised as it was not stored on the affected servers.
It emailed customers early this morning requesting they reset passwords.
"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," the statement said.
"During this process, we learned that data had been illegally accessed from our account database, including user names, email addresses and encrypted passwords."
Ubisoft did not reveal which servers were hacked nor how the compromise took place. In a post it said the attack "did not originate via any Uplay services" and uptime and stability of its gaming services were unaffected.