SINGAPORE - Karaoke chain K Box said it is conducting a full internal probe into the hacking of its membership database, calling the breach a "deplorable act".

The personal data of 317,000 K Box customers was exposed on Tuesday following a security breach, with the firm facing possible sanctions for lax security.

Privacy watchdog, the Personal Data Protection Commission (PDPC), said it is "concerned about the scale" of the alleged breach.

"We are conducting a full internal investigation, and have provided the PDPC and Singapore Police Force with our fullest cooperation," said K Box's Chief Operating Officer Priscilla Ng in a statement issued late Tuesday.

"Steps are being taken to remove the stolen data and hold those responsible for this deplorable act wholly accountable to the fullest extent of the law," she added.

"We wish to assure you that controls and safeguards are in place in protecting your data and we take your data privacy very seriously," she said in the statement.

The leaked data included names, addresses and mobile-phone and identity card numbers, although some are outdated.

K Box members have expressed anger over the leak.

One of them, university student Ms Lee, 20, said she is thinking of making a police report.

"All my private information is in the list. I keep thinking about the things people could do with the information obtained," she told The Straits Times.

"This shows a serious lapse in K Box's security system."

The perpetrators belong to a group which called itself "The Knowns". It sent an e-mail to media outlets, including The Straits Times, on Tuesday morning, saying that it was releasing the data to show its displeasure over recent increases in toll charges at the Woodlands Checkpoint.