Host David Letterman on the set of the "Late Show with David Letterman, in New York. (Heather Wines/AP)

“Is there not among you a Sayyid Nosair al-Mairi ... to cut the tongue of this lowly Jew and shut it forever?” read the message, written by a frequent poster on the message board who goes by Umar al-Basrawi. Al-Mairi killed Jewish Defense League founder Meir Kahane in 1990. Letterman, however, is not Jewish.

Al-Basrawi took particular issue with jokes Letterman had made about Osama bin Laden and Muhammad Ilyas Kashmiri, a senior al-Qaeda leader who was killed June 3.

“The concern is that there is someone who will read it, agree with it and say, 'I want to be the Sayyid Nosair of 2011 and kill David Letterman,’” said Adam Raisman, an analyst for Site Monitoring Service, a private intelligence organization that spotted the post.

This isn’t the first threat for Letterman. In 2009, the talk show host was the target of a $2 million extortion attempt by a CBS News producer, who threatened to expose the host’s sexual relationships with members of his staff.

In 2005, a former painter at Letterman’s ranch in Montana was jailed for plotting to kidnap Letterman’s nanny and son.