Forget about the threat posed by North Korea's missile program. It's already scoring damaging hits on the west with what's known as the "superdollar" - an almost perfect counterfeit US$100 that the rogue nation has been producing by the million and dumping on the world currency market.

One estimate puts the amount Nth Korea makes from counterfeiting more than US$100 million a year.

In November the US put a range of financial sanctions in place against North Korea after the US Treasury revealed it had been using a bank in Macau to put counterfeit currency into circulation. According to US Treasury the bank, the Banco Delta Asia was "a willing pawn for the North Korean government to engage in corrupt financial activities".

The bank, which had links to the North Korean regime stretching back two decades, had accepted large deposits of counterfeit US currency and put them into circulation. The bank had also been used for laundering the proceeds of drug smuggling and counterfeit cigarette sales carried out by front companies set up by the North Korean government, according to the US Treasury.

Shortly after the revelations the Macau Government stepped in and placed administrators in the bank to ensure all connections with North Korea were cut. North Korea broke off international nuclear disarmament talks in November in what was seen as retaliation for the US's sanctions over its counterfeiting and money laundering.

It was also revealed late last year that a Taiwanese national arrested in the US on charges of dealing in counterfeit bills had disclosed to the FBI that North Korea was also using Chinese organised crime groups to distribute its "super dollars".

The BBC has previously reported that "superdollars" are produced on a highly sophisticated printing press, known as the Intaglio, similar to the one used to print money in the US. According to one defector, the notes were produced in a special counterfeiting plant. "We bought the best of everything - the best equipment and the best ink. But we also had the very best people, people who had real expertise and knowledge in the field."

The notes were also distributed by North Korean officials and diplomats when they travelled.

According to the Heritage Foundation, an independent US thinktank, the public naming of the Banco Delta Asia in Macau last year has not stopped the flow of counterfeit notes. It says there's evidence that North Korea has switched to using Chinese state-owned banks in the nearby Chinese Zhuhai Special Economic Zone.

The think tank reported earlier this year that North Korea's printing presses had also been churning out counterfeit Japanese yen, Thai baht, and in recent years, Euros.