Sony has suspended another of its online gaming systems, following the recent PlayStation Network hack.
The company took the Sony Online Entertainment (SOE) service offline as part of its wider investigation into security breaches.
Multiplayer games including DC Universe and Facebook-based Fortune League were unavailable as a result.
Sony admitted last week that the personal details of 77m PlayStation users may have been stolen by hackers.
The suspension of SOE was announced in brief statement on its website, Station.com.
"We have had to take the SOE service down temporarily.
"In the course of our investigation into the intrusion into our systems we have discovered an issue that warrants enough concern for us to take the service down effective immediately. We will provide an update later today (Monday)," it said.
Last week, Sony said that it did not believe SOE users had been affected by the PlayStation Network hack.
A community relations spokesperson wrote on one of Sony's support forums at the time: "We have been conducting a thorough investigation and, to the best of our knowledge, no customer personal information got out to any unauthorized person or persons.
"We are continuing that investigation and monitoring the situation carefully; should the situation change, we will - of course - promptly notify you."
Sony Online Entertainment designs and publishes online multiplayer games for the PC, PlayStation 3 and, in the case of Fortune League, Facebook.
As Sony's investigation continued, the company promised that it would get the PlayStation network up-and-running again this week.
It said users would see a phased re-introduction of gaming, movie and music download services.
PlayStation Network has been unavailable since 20 April.
Sony revealed last week that hackers may have stolen users' personal information, including e-mail addresses, passwords and dates of birth.
It warned that credit card details could also have been taken, but said that particular data was encrypted.