SINGAPORE - Attempts to fix the website of troubled karaoke bar chain K Box after the personal data of over 300,000 customers was exposed on Tuesday have led to the website being intermittently unavailable today.

A company representative said its technical staff has been testing its computer systems, but did not provide details.

The firm, which is possibly facing sanctions for lax security, said late Tuesday night that it is conducting a full internal probe into the theft of its membership database. It has also taken steps to remove the stolen data and links to it from at least three websites.

The leak of K Box's membership database is being investigated by the privacy watchdog, the Personal Data Protection Commission, which said it is "concerned about the scale" of the alleged breach.

Organisations must take "reasonable measures" to protect personal data in their possession, said the commission, citing privacy laws which came into force on July 2. Police investigations are ongoing.

The leaked data included names, addresses and mobile-phone and identity card numbers, although some are outdated. Also exposed were K Box membership numbers and the loyalty points earned. The list included some local celebrities.

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.

It said the hikes were "an unnecessary financial burden on working Malaysians", and threatened to "attack and expose" the databases of more Singapore companies if nothing was done to reverse the charges.