Gaming giant Sony is wrestling with new attacks on its gaming network, just months after a series of attacks brought its systems to a grinding halt and exposed millions of users to potential data theft.

Sony Network Entertainment International LLC and Sony Online Entertainment (SOE) said Tuesday that they have detected "a large amount of unauthorized sign-in attempts" on PlayStation Network (PSN), Sony Entertainment Network (SEN), and Sony Online Entertainment (SOE) services.

"Less than one tenth of one percent of our PSN, SEN, and SOE consumers may have been affected," Sony said in a statement on its website. "There were approximately 93,000 accounts [PSN/SEN: approximately 60,000 accounts; SOE: approximately 33,000] where the attempts succeeded in verifying those accounts’ valid sign-in IDs and passwords, and we have temporarily locked these accounts."

Sony said it will send emails to the affected account holders and will require secure password resets.

Credit card numbers associated with these accounts are "not at risk" as a result of the unauthorized access of accounts, Sony said. "Only a small fraction of these 93,000 accounts showed additional activity prior to being locked," the statement said. "We are continuing to investigate the extent of unauthorized activity on any of these accounts."

The access attempts, which occurred between Oct. 7 and Oct. 10, appear to emanate from one or more compromised customer lists "from other companies, sites, or sources," Sony said. "These were unauthorized attempts to verify valid user accounts on our services using very large sets of sign-in IDs and passwords."

Chris Harget, senior product marketing manager for authentication tool vendor ActivIdentity, suggested that the compromised lists may represent users from another service or network, and that the attackers used the passwords from that list to test the Sony user IDs.

"Some users simplify managing multiple online identities by using common credentials across multiple accounts," Harget says. "The result is that if their gmail or hotmail or Facebook account is compromised, then their eTrade or Citibank or corporate network credentials could be compromised." Two-factor authentication could help mitigate this problem, he says.

Have a comment on this story? Please click "Comment" below. If you'd like to contact Dark Reading's editors directly, send us a message.