Jon Stewart, Stephen Colbert Receive Letters Threatening Biological Attack on Senators

Letters mailed to Comedy Central's Jon Stewart and Stephen Colbert were no laughing matter.

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The messages -- anti-Establishment/Wall Street in tone -- contained language threatening biological attacks on U.S. senators, according to Reuters, citing law enforcement officials. The culprit issued a warning that 10 out of 100 senators would receive a lethal pathogen in the mail.

Meanwhile, a Senate official told Reuters that several letters containing a suspiciously powdery -- but ultimately, harmless -- substance had been sent to goverment offices.

According to The Associated Press, House Speaker John Boehner was targeted along with other politicians at their district and home offices. Besides The Daily Show and The Colbert Report, media organizations such The New York Times, the Los Angeles Times and NPR also received rant-laden, senator-threatening letters signed "the MIB," minus the suspicious powder.

"So far, none of the letters have contained a hazardous substance," FBI Special Agent Jason Pack told the AP on Wednesday. "We are working with those law enforcement agencies affected to determine if the mailings are related. We take these matters seriously and will investigate fully."

A Comedy Central representative did not immediately respond to a request for comment.