Magazine article The American Conservative
Contrary to Mainstream Media Reports, the Threat That Al-Qaeda Was Prepared to Commemorate the 10th Anniversary of the 9/11 Events with a Truck Bombing in Washington And/or New York, Executed by One or Possibly Two Terrorists Holding American Passports, Never Came from a CIA Source
It was based on what is referred to as chatter picked up by National Security Agency off an email from one unknown party to another and was never confirmed by human intelligence or additional electronic intercepts. There was never a human source that was clearly identified in the linkage to the "chatter," and no names were ever developed beyond the suggestion in the message that two of the attackers might be U.S. citizens trained at some terrorist camp in Pakistan. The president had directed U.S. counter-terrorism officials who went public with the threat not to identify the chatter source because he did not want to prejudice the information by revealing that it was a Sigint email intercept.
Sigint is short for signals intelligence, and it includes anything that has been picked up from electronic transmissions. In the intelligence world, Sigint is considered the lowest form of intelligence, as it is similar to what is picked up by a vacuum cleaner, often with no way to establish credibility. Because of the great volume of it, Sigint is unfortunately the principal source of most terrorism-threat information even though it has proven to be highly unreliable and of doubtful value. …