A member of the bank’s staff mistakenly emailed information relating to a number of customers’ accounts to an unrelated customer.
The information that was communicated included the account number and the names of the customers who held that account, together with some other material.
Neither the addresses nor the contact details of the relevant account holders were communicated in the breach, a Permanent TSB said.
Details on the finances of the customers were not communicated either.
The spokesperson added that the affected customers have been contacted and that the bank has apologised for the error.
In a letter sent to an affected customer seen by the Irish Examiner, the bank says the customer who received the information has deleted the mistakenly sent email and has no copies.
The letter also states that the bank has conducted a thorough investigation into the matter and how it occurred.
It has also taken steps to ensure it doesn’t happen again, according to the bank.
The breach is the latest embarrassment for Permanent TSB after the Central Bank uncovered a series of failures relating to customers’ tracker mortgages which led the bank to introduce a redress scheme for some 1,400 affected customers.