Fingers have been pointed in various directions but, according to security researcher Brian Krebs, an Anonymous splinter group is thought to be implicated in the Eidos hack.
The hack, he observes in his latest security blog, comes a few days after Sony told the US Congress that Anonymous members may have been responsible for break-ins on its PlayStation Network and other online services.
"For several hours early Thursday morning, the Deus Ex web site, user forum, and Eidos.com were unreachable. For a brief period late Wednesday evening, the sites displayed a defacement banner that read 'Owned by Chippy1337' along with several names and hacker handles of those supposedly responsible for the break-in", he notes.
Interestingly, Krebs has researched the hack and gained access to an archived copy of the hacker's e-chatter as they were "covering their tracks from compromising the sites."
The hackers, he claims, say they have stolen information on at least 80,000 Deus Ex users and that they plan to release the data on file-sharing networks.
"The attack seems to have been engineered by a faction of the hacker collective that recently seized control over Internet relay chat (IRC) channels previously used by Anonymous to help plan and conduct other, high-profile attacks", says Krebs, adding that the Anonymous control networks were taken over by a 17-year-old hacker from the UK.
According to the security researcher, Anonymous has officially denied being responsible for the Sony breaches.
Meanwhile, he notes, the Financial Times reports that two veterans of Anonymous have acknowledged that members of its group are likely to have been behind the recent hacking attacks on Sony, in spite of the group's official denials.
"It is worth noting that Anonymous seems to be in a state of conflict at a time when Wikileaks appears to be trying to discourage disloyalty among its own sympathisers", he says.