"Originally, the Bureau of Engraving and Printing had planned to exempt the $5 bill and Abraham Lincoln, the 16th president, from the design makeovers introduced over the past three years for the $50, $20 and $10 bills.
But officials said changed their minds in part so they can respond to a new scam in which counterfeiters are bleaching the ink off $5 notes and then printing counterfeit $100 bills on the bleached paper." Associated Press, June 29, 2006
If the counterfeit money concern is $100 bills, why make the $5 bill harder to counterfeit? The counterfeit resistant $100 bill is not scheduled until later than the $5 make-over.