Media reports said the attacks by a so-called Israeli "strike force" targeted sites where the cyberassaults had originated in what Anonymous had claimed would be "the largest Internet battle in the history of mankind."
It was not clear whether the Israeli retaliation, which appears to have been extensive, involved elements of the new military cyber command the Defense Ministry has been putting together under a $320 million program announced in 2012.
But it would make sense for it to be involved in the weekend cyber conflict since the military says the Jewish state, which has reputedly played a major role in repeated high-powered cyberattacks on Iran's nuclear program since 2009, is being increasingly targeted by its Muslim foes.
The military declined comment after the attack Sunday, Israel's Holocaust Remembrance Day, an apparent follow-up to a blitz by Anonymous and its affiliates during Israel's 8-day clash with Hamas in the Gaza Strip in November.
"It's not a military matter," a spokeswoman said.
As it happens, the much-hyped cyberattack, dubbed #opIsrael, and the threat to "wipe Israel off the map of the Internet" announced April 5 on YouTube appears to have been something of a fizzle.
The Bank of Israel and several government sites, including the Education Ministry, the Tax Authority and the Central Bureau of Statistics, were reported to have been briefly shut down or defaced.
Up to 100 other sites, mainly small businesses without security software, were also affected by what Anonymous called the "Hackintifada #Free Palestine," a reference to Palestinian intifadas, or uprisings against Israeli occupation.
Government officials downplayed the impact of the assault. But security sources believe further attacks are likely, and these may be more damaging than Sunday's attempted blitz and may aim for more strategic targets.
The retaliation to Sunday's attacks by an "Israeli Elite Strike Force" appears to have been Israeli hackers acting on their own initiative.
But there have been growing signs that attacks by supposedly independent operators, such as the weekend cyber thrust against Israel, are in fact the work of state actors.
Such attacks, Oxford Analytica observed, "can have a disproportionate impact on international relations ... for motives and aims subversive to international order.
"The greatest danger could emanate from a 'catalytic' cyber attack, whereby a dissatisfied party -- for example, a militant group acting under cover of a third state -- instigates conflict among two other states -- say, the United States and China.
"The capacity of existing conflict management mechanisms to mitigate the risks of such an eventuality does not seem promising," Oxford Analytica cautioned.
In recent months, Israel's military has inaugurated a cyber-defense control center as the Jewish state grapples with a sharp increase in cyberattacks, most of them supposedly from archenemy Iran.
At the same time, Israel's amassing a multibillion-dollar arsenal of electronic weapons to use against the Islamic Republic in a largely covert campaign, but which could come out of the shadows if Israel decides to launch pre-emptive strikes against Iran's contentious nuclear program.
The United States worries about Chinese attacks on its financial and industrial infrastructure. But Israel's focus is almost entirely on Iran.
The Jerusalem Post quoted a senior Israeli military source as saying there's been a dramatic rise in cyberattacks on the digital infrastructure of the armed forces and Iran's seen as the culprit.
"The world of attacks is changing rapidly," he explained as the new center, two years in the planning, became operational in February.
"Few countries have this kind of defense ability," he noted. "This is part of the military's readiness to ensure continuity of conventional operations. This continuity is based on cybersecurity."
Iran, on the receiving end of U.S. and Israel cyber operations, seems determined to enhance its offensive cyber capability, largely to deter the crippling 2009-10 cyber attacks on the uranium enrichment sector of its nuclear program using the Stuxnet worm.
In mid-2012, Western intelligence sources estimated Tehran had spent $1 billion to upgrade its cyber capabilities in less than two years.
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