Eir says that 37,000 of its customers have been affected by a data breach, but that their personal financial details have not been compromised.
In a statement the company say that an unencrypted laptop was stolen offsite on Sunday 12 August, containing the details.
All customers affected are set to be notified today.
The details included the names, email addresses and Eir customer numbers.
The gardaí and the Data Protection Commissioner have been notified about the data breach and theft.
Eir says in its statement : “There is no evidence at this time that the data at risk has been used by a third party.