A weekend cyber attack campaign targeting Israeli government websites failed to cause serious disruption.
The attacks followed warnings in the name of the hacking group Anonymous that it was launching a massive attack.
Yitzhak Ben Yisrael, of the government's National Cyber Bureau, said hackers had mostly failed to shut down key sites.
Posters using the name of the hacking group Anonymous had warned they would launch a massive attack on Israeli sites in a strike they called #OpIsrael.
Israel's Bureau of Statistics was down this morning, but it was unclear if it was hacked.
Media said the sites of the Defence Ministry and the Education Ministry, as well as banks, had come under attack the night before, but they were mostly repelled.
Israeli sites reported brief cyber attacks on the stock market website and the Finance Ministry website last night.
But the two institutions denied the reports.
Israeli media said small business had been targeted. Some homepage messages were replaced with anti-Israel slogans, media said.
In retaliation, Israeli activists hacked sites of radical Islamist groups and splashed them with pro-Israel messages, media said.
Hackers have tried before to topple Israeli sites.
"So far it is as was expected, there is hardly any real damage," Ben Yisrael said.
"Anonymous doesn't have the skills to damage the country's vital infrastructure," he said.
"And if that was its intention, then it wouldn't have announced the attack ahead of time.
"It wants to create noise in the media about issues that are close to its heart," he said.
In January last year, a hacker network that claimed to be based in Saudi Arabia paralyzed the websites of Israel's stock exchange and national airline and claimed to have published details of thousands of Israeli credit cards.
A concerted effort to cripple Israeli websites during November fighting in Gaza failed to cause serious disruption.
Israel said at the time that protesters barraged Israel with more than 60 million hacking attempts.
An official of the militant Hamas movement that rules the Gaza Strip praised the current attack. "God bless the minds and the efforts of the soldiers of the electronic battle," Ihab Al- Ghussian, Gaza's chief government spokesman, wrote on his official Facebook page.