A couple of weeks later, an Iranian news agency claimed that 300 Shiite websites had been defaced by Wahhabis, as the austere Sunni Muslims in Saudi Arabia are known, including that of Mr. Sistani, Iraq's top Shiite cleric.
Then came attacks on scores of Sunni websites. Shiite hackers often left the same calling card: a face painted with the colors of the Iranian flag, and a map of the Arabian Gulf labeled "The Persian Gulf."
Hacking Al Qaeda
Meanwhile, another noteworthy cyber-event occurred in early September, when several online forums affiliated with Al Qaeda were knocked out of commission. So far, they have not been revived.
"It's unprecedented, because before they've been able to come back [within] a few days," says William McCants, a Washington area-based analyst of militant Islam and founder of jihadica.com, which monitors Al Qaeda Web activity.
Mr. McCants says that in June, he noticed that a prominent Al Qaeda forum had disappeared. It came back in a few days but then shortly before Sept. 11, it and several other forums went down. "It seemed like June was a test run."
Private groups involved in countering online terrorist activity have denied responsibility and US intelligence agencies declined to comment, Kohlmann says in an e-mail, adding, "I would say this much: It certainly does not appear to be a coincidence that the forums encountered these technical problems on September 10."