Cayman National Corporation (CNC) has confirmed that customers' names, addresses and account details were among the data stolen from its Manx-based bank and trust company.
The massive data breach was reportedly carried out by hacktivist Phineas Fisher also known as HackBack.
The hacker published over 2TB of data belonging to the bank's 1400 customers including roughly 640,000 emails. Almost half of the customers are registered at the Cayman National Bank (Isle of Man). The data includes complete addresses of the customers, and balance information and owner names of 3800 bank accounts.
The Cayman National bank and Trust confirmed hacking of "raw" data from its database while sharing an internal document containing details of the hack attack. However, the scope of "data hack" is yet to be explained by the bank.
The bank warned stolen details could be used for "fraudulent purposes" and said it would contact customers affected. Authorities on the island have launched an investigation into the attack.
The Manx bank and trust company are subsidiaries of CNC, which is based in the Cayman Islands.
According to reports, Phineas Fisher is one of the most influential and well known hacktivist groups. Their identities have never been made public and European law enforcement agencies admit they have no idea who they are.
Isle of Man Chief Minister Howard Quayle said he would be working with Manx authorities "to understand what happened and what lessons can be learned".