GARDAí tried to negotiate the return of the laptop which was stolen from Bord Gáis offices and contained personal details of more than 75,000 customers. Officers believe the computer was taken in an opportunistic raid at the company's premises on Foley Street in Dublin's north inner city.

The laptop was one of four taken during the raid, which took place in the early hours of Friday, 5 June. It contained details of customers who had moved from ESB as part of the Big Switch campaign, including account numbers, home addresses and bank branch details.

A number of young criminals in the area have been identified as prime suspects but detectives believe the portable computer was probably sold on within a matter of days. Sources said it had been made known to likely suspects in the area that the computer could be returned to halt the security breach. Gardaí said it was likely the laptop had already been pawned or sold off to a second-hand computer dealer, where its hard-drive would have been wiped clean and reformatted.

One garda source said: "The criminals who stole this computer had no idea what they were getting their hands on; nor would they be the type that would be in a position to take advantage of personal details like that."

Although the computer was not encrypted, it was password-protected and Dave Bunworth, the managing director of Bord Gáis Energy, said it would "be very difficult to get into". A spokeswoman for Bord Gais confirmed the computer was encrypted and all its machines were now fully secure.

Bord Gáis came in for criticism after it emerged it knew about the theft for almost two weeks before letting customers know what happened. The company went public with the robbery on Wednesday, 12 days after the computer was stolen. It is also understood Bord Gáis hired a group of private investigators to find the laptop.