Abbey's Internet banking service was hit by a technical glitch on Thursday evening which resulted in some users randomly shown data belonging to other customers.
In a statement the bank says it experienced system problems relating to its e-banking facility "as a consequence of network issues with our external supplier".
The problem is thought to have occurred between 6pm and 11pm on Thursday.
Abbey says there was a "short window" where customers could view random data. But the bank insists that none of the data related to a specific customer and none could be "transacted on". The bank says it was "a presentational error without any security exposure".
"Our security alerts were triggered and we immediately responded by removing the service to correct the issue. Services were fully available by 11pm last night," says the statement.
Abbey was hit by a series of embarrassing computer mishaps last year as it undertook the phased roll-out of a new banking platform from Spanish parent Banco Santander.