According to the AP's Ted Bridis, who describes this as being "high on the creepiness scale," the U.S. Department of Defense has warned its contractors to be wary of Canadian coins, suggesting that some coins have been modified with embedded RFID tags in order to track people. "The government said the mysterious coins were found planted on U.S. contractors with classified security clearances on at least three separate occasions between October 2005 and January 2006 as the contractors traveled through Canada," Bridis writes.

The DoD, apparently, isn't sharing much more info than that. But Bridis says other experts say logical suspects are China, Russia and France, countries that are "said to actively run espionage operations inside Canada with enough sophistication to produce such technology."

Still, there are a few rather obvious holes in the plan, not the least of which is the fact that a coin isn't the best place to hide tracking technology. "It wouldn't seem to be the best place to put something like that; you'd want to put it in something that wouldn't be left behind or spent," says writer Jeff Richelson. "It doesn't seem to make a whole lot of sense."

And perhaps it doesn't -- The Globe and Mail's Colin Freeze says the intelligence may not be completely correct. "Defence contractors had apparently been given certain special-issue Canadian coins, the unfamiliar look of which caused them to be concerned about the money, a source said," Freeze writes. "That led to an investigation once the contractors returned to the United States. But a U.S. agency that investigated the complaint found no evidence of any secret transmitters, or of any other tampering."