Washington ? After six decades in which the venerable greenback never changed its look, the U.S. currency has undergone a slew of makeovers. The most amazing is yet to come.

A new security thread has been approved for the $100 bill, The Associated Press has learned, and the change will cause double-takes.

The new look is part of an effort to thwart counterfeiters who are armed with ever-more sophisticated computers, scanners and color copiers. The C-note, with features the likeness of Benjamin Franklin, is the most frequent target of counterfeiters operating outside the United States.

The operation of the new security thread looks like something straight out of the Hogwarts School of Witchcraft and Wizardry. This magic, however, relies on innovations produced from decades of development.

It combines micro-printing with tiny lenses – 650,000 for a single $100 bill. The lenses magnify the micro-printing in a truly remarkable way.

Move the bill side to side and the image appears to move up and down. Move the bill up and down and the image appears to move from side to side.

“It is a really complex optical structure on a microscopic scale. It makes for a very compelling high security device,” said Douglas Crane, a vice president at Crane & Co.

The Dalton, Mass-based company has a $46 million contract to produce the new security threads.

Larry Felix, director of the Bureau of Engraving and Printing, confirmed details about the security thread in an AP interview.

The redesign of the $100 is about one-third of the way complete. The bill is expected to go into circulation late next year.

Starting in 2003, splashes of color have spruced up the $20 bill and other currencies. Those changes followed the addition of a first round of security features in the mid-1990s.

Benjamin Franklin’s latest makeover was delayed while the government searched for a high-tech security device that would provide extra protection on the bill.

The $100 bill represents more than 70 percent of the $776 billion in currency in circulation, two-thirds of which is held overseas.

Holograms, used extensively on credit cards, were considered for the $100.

They were rejected because they did not offer the strong visual signal the government wanted.

“We were looking for features that had very distinctive types of actions so that we could tell the American public, you will know that it is authentic if you do this and the note does that,” Felix said.