A number of other high-profile companies are now thought to have been caught up in the hacking incident at Clare firm "Loyalty Build".
Some customers of Clerys, Centra, Stena Line and Postbank may have had their details compromised.
However, the numbers involved are far smaller, believed to be in the hundreds.
The hack, blamed on "sophisticated criminals", happened in mid-October.
The company involved, LoyaltyBuild, is expected to release a further statement this evening.
In a statement this evening, Centra said it has "no ongoing relationship with Loyalty Build."
"Centra’s involvement dates back to 2006 and affects 68 people who availed of a promotion to collect vouchers toward city breaks in European destinations," the company said.
"The only data that is potentially compromised is personal data which includes names and addresses."