The Counterfeit Dollars market consists of producing and utilizing currency that was not created under the authority of the United States Government.
$61 million counterfeit dollars were passed into circulation.
Source: United States Treasury Department, ” The Use and Counterfeiting of the United States Currency Aboard, Part 3” , Final Report to the Congress by [...]

United States Authorities have seized around 50 Million Counterfeit Dollars known as Supernotes that originated from North Korea.
Source: AP, “U.S. fights N. Korea efforts to forge currency,” MSNBC.com, August 7, 2006,(accessed: September 3, 2006).

Source: Korea Times, “NK Earns $20 Million a Year From Counterfeiting: Expert” , May 15, 2005.

The US Treasury announced Congressional testimony that it was still investigating counterfeit dollars known as “Supernotes” believed to originate from North Korea.
From Reuters:
Turning to North Korea, Levey said the U.S. Secret Service was continuing to investigate counterfeiting activities by Pyongyang. He said high-quality counterfeit $100 bills produced by North Kora, known as the “Supernote”, were [...]

The Los Angeles Times has a photo gallery of the new $5 bill.
See the new characteristics here.  
The new bill went into circulation last week.
$61 million counterfeit dollars were passed in the United States.

A man in Arizona attempted to use 2 counterfeit $100 bills with the image of Abraham Lincoln on it. As Americans are well aware, Abraham Lincoln is on the $5 bill, while Ben Franklin is on the $100 bill.
From CBS Affiliate KPHO in Arizona:
A 37-year-old Mesa man who tried to buy a watch with [...]

An unknown couple in Colorado passed a counterfeit $100 bill when purchasing Girl Scout Cookies outside of a local supermarket.
From ABC Affiliate in Colorado The Denver Channel.com:
Westminster police issued a warning about the dangers of counterfeit money Sunday after a Girl Scout group reported they unknowingly accepted a fake $100 bill for cookies.
The girls [...]

McClatchy Newspapers has a report on the counterfeit $100 “Supernote” and the problems that it is causing the United States government.
Aspect of the bill that causes concern:
•The paper appears to be made from the same cotton and linen mix that distinguishes U.S. currency from others. It includes the watermarks visible from the other side of [...]