(CNN) -- The Web site of Iraq's most influential Shiite cleric was hacked on Friday, with the attackers' messages saying they are Sunnis upset over fatwas, or edicts, issued on the site.

A entity called Group XP placed a video of comedian Bill Maher making fun of Ayatollah Ali al-Sistani and his advice to the Shiite faithful, as well as posting messages on the site.

The hackers said they are upset at the sexual nature of the advice given to faithful allegedly by al-Sistani through a spokesperson. Those who have studied the attack believe that the Maher video is meant to illustrate how such advice promotes mockery of Islam.

The communications said it was hacking this and other sites giving a "bad name" to Sunnis. The messages said Christian sites that insult Islam and sexually oriented sites run by Arab Christians out of Israel were also hacked. Watch what visitors to the Web site saw »

"We have hacked this site, the head of strife and division that many lost souls," the message said. "Farsis and their likes, depend on for guidance."

News reports link the hackers to Wahhabis, fundamentalist Sunnis who prevail in Saudi Arabia.

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