Jerusalem (CNN) -- A group claiming to be Saudi Arabian hackers is posting the credit card information and other identifying data of thousands of Israelis online, prompting an international investigation.
The group first posted a message Tuesday, which included claims that 400,000 credit card numbers had been published.
"Hi, it's OxOmar from group-xp, largest Wahhabi hacker group of Saudi Arabia," read a statement posted on an Israeli sports website the group hacked into. "We are anonymous Saudi Arabian hackers. We decided to release first part of our data about Israel."
The Bank of Israel released a statement Tuesday saying that based on information from credit card companies, only about 15,000 credit card numbers were exposed, and those cards were blocked for use in Internet and telephone purchases.
Thursday, the group claimed to have released another 11,000 credit card numbers and threatened to publish many more.
Yoram Hacohen, the head of the Israeli Law, Information and Technology Authority at the Israeli Ministry of Justice, told CNN in a phone interview Friday he's more concerned about the private information that was released, not the credit card numbers.
The publishing of information such as e-mail addresses, phone numbers, home addresses and passwords could lead to identification theft, he said.
Hacohen said the hacking is a criminal act against citizens of the world, since some of the information exposed belongs to Jews worldwide, not only Israelis.
Israeli authorities have begun a criminal investigation, including a computer forensic probe to search for electronic evidence to try to locate the group, Hacohen said. The theft of personal information is a criminal act under Israel's Privacy Protection Law.
He acknowledged that in the digital world, offenders are very difficult to track, and authorities are asking for international help in the matter.
"The peculiar incident we are facing could be a bad joke, a youthful prank, a hate-driven terror attack for beginners or the cellars of the Iranian intelligence in Tehran," wrote Israeli columnist Ben Caspit in the Maariv newspaper Friday, outlining the difficulties of trying to identify the hackers.
Israeli Prime Minister Benjamin Netanyahu created a National Cyber Headquarters in May 2011, noting the emergence of cyber attacks that could "potentially paralyze life systems -- electricity, communications, credit cards, water, transportation, traffic lights."
He said in December that the new agency -- along with a rocket defense system and a physical fence -- would help protect Israel against its enemies.
An official with the prime minister's office said the National Cyber Headquarters is currently in the process of being set up.