Hackers have attacked the websites of Israel's stock exchange and national airline in a deepening cyber war launched earlier this month by a group claiming to be Saudis.

Neither website contains sensitive information and trading and flights were not affected. But the continuing raids by hackers who use anti-Israel language in their posts has revealed how vulnerable Israel is to cyber warfare, despite its sophisticated computer security units in the military and advanced high-tech sector.

The attacks began earlier this month when hackers identifying themselves as group-xp, a known Saudi hacking group, claimed on an Israeli sports website to have gained access to 400,000 Israeli credit card accounts. The group called it a "gift to the world for the New Year" designed to "hurt the Zionist pocket."

Israeli authorities said 15,000 accounts were hacked in that episode and credit card information about 6,000 other Israelis was disclosed online a few days later by the same network.

Last week, an Israeli hacker identifying himself as a soldier in an Israeli intelligence unit retaliated by posting information online about hundreds of Saudis, Egyptians, Syrians and others.

El Al Israel Airlines took down its website after the alleged Saudi network linked to previous attacks warned that both sites would be targeted by allied pro-Palestinian hackers, a source close to the company said.

The company said it was taking security measures to protect the website and that disruptions on the site were to be expected.

A spokeswoman for the Tel Aviv Stock Exchange, said the site was overwhelmed by electronic requests that slowed it down dramatically but it was still operating. Trading was not affected.

Cyber experts say Israel is a common target for online attackers. There have been no confirmed reports of sensitive Israeli government sites being hacked. Several weeks ago, websites of Israeli spy services and other official sites briefly went down, but the government denied hackers were to blame and characterised the event as a technical malfunction.

Israel is a world leader in cyber security, and the Shin Bet internal security agency provides advisory services to sensitive business sectors such as banks and public utilities.