The hackers said their operation "OpIsrael" had either damaged or completely erased the databases of more than 650 private and public institutions, including the Bank of Jerusalem -- one of Israel's main finance houses.
"Bank of Jerusalem database has been deleted," the group said in a tweet next to a link to the lender's non-functioning website.
It also claimed to have briefly taken down the foreign ministry website in protest over an alleged Israeli threat to cut the Gaza Strip's internet communications.
"For far too long, Anonymous has stood by with the rest of the world and watched in despair the barbaric, brutal and despicable treatment of the Palestinian people in the so called 'Occupied Territories' by the Israel Defence Force," Anonymous said in a statement.
"But when the government of Israel publicly threatened to sever all Internet and other telecommunications into and out of Gaza they crossed a line in the sand."
The group threatened Israel with the "unbridled wrath of Anonymous" if it went ahead with the internet cable cut.
Israel's foreign ministry was not immediately available for comment on the threat and no reference to the hack attack was made in official government statements on Saturday.
Israel has been pressing an intense aerial assault over the coastal Palestinian enclave as militants from the ruling Hamas movement and other groups have reportedly retaliated with hundreds of rockets over the border.
The intensifying stand-off has also played out over the Internet. Militants have used social networking sites such as Twitter to promise new attacks and take credit for specific strikes.
Meanwhile, Israeli defence officials have used Twitter to provide real-time warnings about incoming rockets and also make direct threats against Hamas.
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Bravo Anonymous!! Pakistan should hand over its nuclear remote control to you guys. Just be responsible with it.
Great work by anonymous.......
Looks like all the Pakistani TV are getting good paid for not highlighting israeli terrorism to Pakistan public.
Shame on Pak media as they have lost all their credibility and respect and now working just for their US and westerner masters to get more bone of dollars to lick.