Espionage warnings from the Defence Department caused an international sensation a few years ago over reports of mysterious coins with radio frequency transmitters, until they were debunked.
The culprit turned out to be a commemorative quarter in Canada. But at the height of the mystery, senior Pentagon officials speculated whether Canadians were involved in the spy caper.
In sensational warnings that circulated publicly in late 2006 and early 2007, the Pentagon's Defence Security Service said coins with radio transmitters were found planted on U.S. Army contractors with classified security clearances on at least three separate occasions between October 2005 and January 2006 as the contractors travelled through Canada.
In January 2007, the government abruptly reversed itself and said the warnings were not true. The case remained a mystery until months later, when AP learned that the flap had been caused by suspicions over the odd-looking Canadian "poppy" quarter with a bright red flower.
The silver-coloured 25-cent piece features the red image of a poppy - Canada's flower of war remembrance - inlaid on a maple leaf.
What suspicious contractors believed to be "nanotechnology" on the coins actually was a protective coating the Royal Canadian Mint applied to prevent the poppy's red colour from rubbing off. The mint produced nearly 30 million such quarters in 2004 commemorating Canada's 117,000 war dead.