The familiar pictures of Founding Father Ben Franklin is still there, but there are a lot of new high-tech features being put in the new $100 bill, including a moving microprint that "looks like something straight out of the Hogwarts School of Witchcraft and Wizardry":
The blue 3-D Security Ribbon on the front of the new $100 note contains images of bells and 100s that move and change from one to the other as you tilt the note. The Bell in the Inkwell on the front of the note is another new security feature. The bell changes color from copper to green when the note is tilted, an effect that makes it seem to appear and disappear within the copper inkwell.
“The new security features announced today come after more than a decade of research and development to protect our currency from counterfeiting. To ensure a seamless introduction of the new $100 note into the financial system, we will continue global public education of retailers, financial institutions and industry organizations to ensure that consumers and merchants are aware of the new security features,” said Treasurer of the United States Rosie Rios. (Source)
Why the redesign? While security and protection against forgery is always a concern for any currency, the failure of the US Government to stem the rise of the Superdollar - a counterfeit so well done that it's almost impossible to detect - is to blame.