Sony said hackers stole details belonging to hundreds of its mobile unit clients, the latest in a string of cyberattacks to hit the embattled Japanese electronics giant.
The attack is the latest cyberattack to dog struggling electronics giant Sony.
A group calling itself "Null\Crew" said it had attacked a mobile communications server, with a Sony spokesman said on Thursday, confirming the cyber thieves had grabbed information belonging to 400 customers in mainland China and Taiwan.
Null\Crew, which reportedly has links to international computer hacking group Anonymous, posted online usernames, e-mails and some passwords along with a statement critical of the Japanese firm, AP reports.
"Sony, we are dearly disappointed in your security," it said, adding that it had gained control of eight Sony servers, which could not be immediately confirmed.
"Not even your customers can trust you," it added.
The company spokesman said the incident was being investigated and added that the server with client details belonged to an unnamed "third party", and not Sony itself.
In April last year Sony suffered a massive data breach that compromised more than 100 million accounts and forced it to temporarily halt its PlayStation Network and Qriocity services.
And in October, the firm suspended 93,000 accounts on its online entertainment networks, which let users play videogames and watch movies, after detecting a wave of unauthorised sign-in attempts.
The entertainment giant has been battling to restore consumer trust after the initial security gaffe, with a string of subsequent attacks on websites including in Greece, Thailand and Indonesia.
In another incident, a group of hackers known as Lulz Security in June said they had compromised more than one million passwords, email addresses and other information from SonyPictures.com.