The letter containing a potent grade of highly concentrated anthrax and sent to Senator Tom Daschle of South Dakota bore strong similarities in language and handwriting to the letter sent to “NBC Nightly News” anchor Tom Brokaw. The sender or senders of the letters remains unknown. Officials, however, have stopped short of linking outright the letters to international terrorism, notes The New York Times, but the gravity of the threat immediately transformed the investigation into a serious national security concern. In reaction to the understandable collective national case of jitters, CBS has yanked Thursday’s episode of “The Agency” because of its storyline. The episode was to have dealt with a CIA effort to fight an anthrax threat to the U.S. “We certainly don’t want to do anything to add to the country’s fears about anthrax,” network spokesman Chris Ender told the Associated Press on Tuesday. In the past two weeks, anthrax has been discovered in three states and Washington, D.C. Tests have shown that at least 13 people either have the disease or were exposed to its spores. One person has died. “The Agency” episode originally was to air Sept. 27 but was pulled after the Sept. 11 terrorist attacks. It was among a number of changes networks made in the wake of the tragedy. The anthrax episode was rescheduled to air Oct. 11 but was bumped that night by President Bush’s primetime news conference. Rescheduled to this week, it has now been postponed indefinitely.