According to Entertainment Weekly, SITE Intelligence Group, a private company that tracks extremist activity on the web, said a frequent commenter on Shumukh-al-Islam, a site that frequently received messages from Al Qaeda in the United States, has called on Muslims to kill the CBS talk show host. Why? EW reports Letterman mocked the death of accused terrorist leader Ilyas Kashmiri.

Kashmiri was killed by a US airstrike in Pakistan in June 2011.

"Is there not amongst you a Sayyid Nosair al-Masri (may Allah release him) to cut the tongue of this lowly Jew and shut it forever," a poster who calls himself Umar al-Basrawi wrote. "Just as Sayyid (may Allah release him) did with the Jew Kahane."

Letterman is not Jewish. The threat refers to the murder of Rabbi Meir Kahane, which Sayyid Nosair al-Masri was tried for in 1990.

A SITE analyst advised Letterman to take the same amount of precaution he would normally take with an obsessed fan.