A hacker claiming to be a 19-year-old Saudi posted thousands of Israeli credit card numbers and other personal data online earlier this week the hacker's second politically motivated attack this year.
In response, the Israeli government likened the action to "a breach of sovereignty comparable to a terrorist operation, and must be treated as such," according to Reuters.
Deputy Foreign Minister Danny Ayalon said in a speech that Israel had not yet ruled out the possibility that the hacking had been carried out by a group "more organized and sophisticated ... than a lone youth," Reuters reports.
The hacker released the details of some 6,000 active accounts late Thursday, on top of the 15,000 made public earlier in the week, said Yoram Hacohen, the head of Israel's data protection agency.
The hacker claims to have published details about 400,000 Israelis and blamed the "Zionist lobby" for covering up the size of the leak, in remarks published on the Internet on Thursday.
"I've hacked much more than you can imagine," wrote the hacker, who goes by the pseudonym 0xOmar and affiliates himself with group-xp, a known Saudi hacking group.
He claimed that he collected close to a million Israeli credit card numbers and would soon publish them all.
Hacohen called it a "cyber crime," and the head of the Israeli Visa CAL company, Israel David, told Israel Army radio it was a "technological terror attack on the citizens of Israel."
Credit card companies say only a few hundred dollars had been fraudulently spent on the hacked cards. They said they swiftly closed affected accounts and were boosting their staff for the weekend in case more data is released.
The governmental data protection regulator was more worried about Israelis' personal details, like ID numbers, email addresses and passwords, which were also posted online and that could be used by identity thieves.
Israelis weren't the only ones affected. Hacohen said personal data belonging to a few hundred people around the world, who purchased Jewish art and objects on an online site, was also compromised.
Hacohen said his agency was investigating the case and was considering asking Interpol for assistance in apprehending the hacker. He also called on "good hackers" around the world to assist Israel in catching the offender.