The ADL Web site was taken over for about 20 minutes Tuesday by hackers who identified themselves as the "World's Fantabulous Defacers." In lieu of the ADL home page, the attackers posted threats to Israelis as well as pro-Palestinian sentiment. The hackers did not gain access to any sensitive information.
The group closed the site a few minutes after the attack was discovered, according to an ADL representative. Four hours later, the site was restored.
New York law enforcement is investigating the incident.
ADL national director Abraham H. Foxman said the organization, which fights against anti-Semitism, was concerned but not surprised about the incident.
The ADL "has become the latest target in what has apparently become an aggressive cyberwar being waged against pro-Israel organizations in both the United States and in Israel," he said in a statement.
"The Internet has clearly become a new weapon in the arsenal of cyberterrorists who wish to derail the peace process and prolong Palestinian violence by attempting to muzzle groups who speak out in support of Israel," he added.
Middle East violence has been fueling an online cyberwar as hackers from both sides of the conflict threaten government and private-sector Web sites in Israel and the United States.
In the last several months, at least 24 sites have been hit by pro-Palestinian attackers, and at least 15 sites have been hit by pro-Israeli attackers, according to iDefense, a Fairfax, Va.-based company that has been monitoring the cyberattacks by pro-Palestinian and pro-Israeli groups.
Among those hit were the sites of the Bank of Israel, the Israeli Prime Minister, the Tel Aviv Exchange Market and the Israeli Foreign Ministry. Palestinian sites have included those of the Palestinian National Authority--the official Palestinian government body--and the Palestinian organization Hamas.
The FBI has warned in recent months that the U.S. government and business Web sites are potential targets, after the battery of attacks on both Israeli and Palestinian Web sites.
The ADL does not know if Tuesday's incident is linked to others.