Most of us will only get $100 bills from a bank, but if you work retail you might get scammed. The showed how they did it on Dateline. They take $5 bills and remove the ink. Then they photocopy a $100 bill over the paper. This way if you only rub one of those pens that detect counterfeit money it will still show up as money, they only mark black on paper. Visually you can still tell because they said that the Lincoln watermark stays. Also the security strip will still say $5 and be in a different location than on the $100 bill. They didn't mention it but on the lower right hand corner the $100 symbol should not be reflective and change tones on the counterfeit.