Creating an Android app named "UltraReset" and using it in tandem with an NFC-enabled Android phone (a Nexus S, in this case), security researchers Corey Benninger and Max Sobell were able to reset and reuse -- free of charge -- transit access cards in both San Francisco's MUNI system and New Jersey's PATH system.

ENGADGET: Security researchers identify transit system exploit in San Fran and New Jersey, create app to prove it