Some time ago we wrote about vulnerabilities in RFID cards. Our reader Robert sent us an e-mail about an interesting report published by the University of Massachusetts.
Researches tested various RFID-enabled credit cards and were able to launch a series of attacks against them, with home made equipment. Scary!

You can download the whole paper from http://prisms.cs.umass.edu/~kevinfu/papers/RFID-CC-manuscript.pdf.