Remember the ugly feeling you used to get in the pit of your stomach after 9/11 every time a new video message from Osama bin Laden or his top deputy, Ayman al-Zawahiri, appeared on TV? One reason we became conditioned to dread these spectral broadcasts was that the government itself told us to be frightened: Bush administration officials quietly, and sometimes not so quietly, spread word that the bin Laden videos, which usually made their way to the outside world via the Arabic satellite news channel Al-Jazeera, could contain secret messages to Qaeda "sleeper cells," signaling them to proceed with long-planned attacks against American targets. If you think back carefully, no American official ever produced convincing proof that the videos actually contained hidden messages from bin Laden. But nobody ever conclusively demonstrated that they didn't.

Now, however, Aram Roston, a former network-news investigative producer and biographer of Iraqi political manipulator Ahmed Chalabi, reports that some of the Bush administration's paranoia about hidden terrorist messages was the work of a con man. According to a long article Roston has just published in Playboy, at least some of the government's concern about the alleged secret Al-Jazeera messages was the product of a sales job by a now-bankrupt "self-proclaimed scientist" who managed to get the government to pay him for computer software that he claimed could unravel hidden "bar codes" embedded in Al-Jazeera's broadcast signal.

Working first with a software company headed by a former associate of fallen junk-bond king Michael Milken and later with the financial backing of a wealthy Washington, D.C., socialite, Roston says that Dennis Montgomery claimed, with no supporting evidence, to have produced intelligence that sparked several memorable government terror alerts.

Sooner or later, most if not all of the agencies that he was dealing with concluded that Montgomery, who had no real training in cryptography or computer science, was peddling bunk, and they terminated his contracts. The CIA, which felt compelled, like much of the rest of the government in the wake of 9/11, to take a serious look at any possible sources, however outlandish, for intelligence on forthcoming attacks (particularly plots against airliners), didn't take too long to conclude that Montgomery's science was dubious. Roston reports the agency showed him the door five years ago after its scientists, working with counterparts in French intelligence, concluded that Montgomery's claims about hidden Al-Jazeera messages could not be substantiated. But Roston says other agencies continued to bite, with the Pentagon signing a contract with Montgomery as recently as January 2009. Two lawyers representing Montgomery did not respond to messages from NEWSWEEK requesting comment. The CIA declined to comment.