Crytek has taken a number of its websites offline following "suspicious activity", and warned that registered users will be asked to change their password the next time they log in.
In a message posted on its official website, the developer said that it had "recently [become] aware of suspicious activity relating to some of Crytek's websites, and acted quickly to take those websites offline for security reasons.
"We thank you for your patience, and expect to have these sites fully operational soon."
Crytek.com, mycryengine.com, crydev.net, and mycrysis.com each currently display the message, although crysis.com, gface.com and warface.com appear to have been unaffected.
The notification suggests Crytek may have become the latest target of hackers, following similar "unauthorised access" discovered in Ubisoft's network last month.
Crytek is currently developing Xbox One launch title Ryse.