Israeli authorities have described a cyber attack last week as "a terrorist operation".
The Bank of Israel's Banking Supervision Department confirmed that the information from around 15,000 active accounts had been exposed on 3 January, while two days later a second list of around 11,000 credit card numbers were published online.
According to the statement by the hacker ‘0xOmar', more than 400,000 records including names, addresses, Israeli ID numbers, telephone numbers and credit card numbers including expiry dates and CVV numbers were released. 0xOmar said he had one million Israeli social security numbers and, upon seeing a reaction, would release the rest.
The hacker identified himself as being "from group-xp", the "largest Wahhabi hacker group of Saudi Arabia" and "the Saudi Arabia hackers of Anonymous hacking movement". He said he enjoyed "watching 400,000 people gathered in front of Israeli credit card companies and banks, complaining about cards and that they are stolen", and "watching Israeli banks shredding 400,000 credit cards and re-generate new cards".
The Banking Supervision Department said it had identified the customers whose credit card details were exposed on the internet. These involved three credit card companies: Cal (Cartisey Ashrai Le'Israel) Israel Credit Cards; Isracard; and Leumi Card.
It said in a statement: “The Banking Supervision Department is in continuous contact with the companies in order to investigate the event, the circumstances of its occurrence, and actions being taken to deal with the occurrence.
“The credit card companies reported that they have identified the cards of the customers whose details were exposed on the internet and the cards have been blocked for use in Internet purchases and telephone purchases. This is expected to prevent fraudulent use of the cards through these methods, following the exposure of the information.
“The companies are contacting the customers in order to exchange the cards that they own. Service centres of all the companies are set to provide answers to customers and customers who suspect that their card has been misused can turn to the credit card company in order to look into the need to cancel the charge.”
Talking to BBC News, Israeli deputy foreign minister Danny Ayalon said such cyber attacks are "a breach of sovereignty comparable to a terrorist operation, and must be treated as such".
He said: “Israel has active capabilities for striking at those who are trying to harm it, and no agency or hacker will be immune from retaliatory action.”
It has also been claimed that 0xOmar may be a 19-year-old living in Mexico; however, according to a report by the Jerusalem Post, 0xOmar stated that it was impossible to find him and that he knows how to disguise himself.