Bord Gáis electricity users who signed up to the company over the past four months have been urged to check their bank accounts to ensure they have not been defrauded.
The call came from Bord Gáis Managing Director David Bunworth, who revealed that confidential data on 75,000 customers was contained on a stolen laptop.
Mr Bunworth apologised unreservedly to the customers affected and said all the company's laptops were now encrypted.
It is understood the confidential information was held on one of four laptops stolen from the offices of Bord Gáis nearly two weeks ago.
Bord Gáis did not publicise the incident until yesterday as gardaí were investigating a particular line of inquiry.
One of the computers was not encrypted.
The incident occurred early on Friday 5 June when the Bord Gáis offices in Dublin and a number of adjacent offices were burgled.
While Bord Gáis will not comment directly on which customers were affected, the information did relate in part to people who recently switched over from the ESB in the company's Big Switch campaign.
In a statement last night, Bord Gáis said gardaí and the Data Protection Commissioner were immediately informed and a full investigation is currently under way.
It added any customers affected by this will be contacted by Bord Gáis Energy directly early next week.
However, speaking on RTÉ's News at One, Data Protection Commissioner Billy Hawkes said his office had learned only one week after the theft that the information had not been encrypted.
Mr Hawkes said his office informed Bord Gáis in the last two days that formal enforcement action would be taken if it did not immediately tell its customers about the theft.
