The Sun has warned customers their data may have been stolen during the hacks on the newspaper's website in July.
Data taken included details on those who took part in competitions and polls on the Sun website, which was hacked on 19 July.
LulzSec claimed it was behind the attack, which led visitors to a fake story about Rupert Murdoch dying.
Last night an email was sent out by Chris Duncan, director of customer management at News International, saying compromised data could have included name, address, date of birth, email and phone numbers.
"No financial or password information was compromised," he added.
"We are contacting you because we believe that information that you submitted to us could have been accessed, and may be published online by the group responsible."
A hacker going by the name of Batteye claimed responsibility for taking the data, whilst indicating he or she has no ties to either Anonymous or LulzSec.
"We will begin today be presenting to you, various files obtained from The Sun, a company within the News Corp group," a message from Batteye on Pastebin read.
"We will continue, until the list has been exhausted, or until the world and man kind realizes that we must change how we go on."
Batteye's claim of the hack has potentially thrown into doubt who was responsible for the original compromise.
LulzSec and Anonymous have been reticent about releasing data they claimed to have taken from The Sun. However, sources have indicated a release could be imminent.
The Information Commissioner's Office (ICO) has said it will be looking into the data breach at the Sun.
"We have recently been informed of a possible data breach which appears to involve the website operated by the Sun newspaper," a spokesperson said.
"We will be making enquiries into the circumstances of the alleged breach of the Data Protection Act before deciding what action, if any, needs to be taken."
