Security Feature Strength of the US Dollar
From a 2003 FRB paper:
“The U.S. dollar, especially its pre-1996 series, had significantly fewer counterfeit protection devices than many other industrialized countries … However … the technology embedded in the new-design 1996-series $100 approached that of other countries’ currency at that time. The technology of Euro banknotes, which were introduced in 2002, is generally higher than the 1996-series U.S. dollar, but the new-design $20 issued in October, 2003 has comparable security to the Euro.
Emphasis mine. Source: 2003 FRB paper.