Sniff, I miss Black Hat... Here's a bit from SANS Newsbites:

RFID Tags are Not Developed with Security in Mind
(28 July 2004)

Speaking at the Black Hat Briefings conference, Lukas Grunwald, CTO of DN-Systems Enterprise Internet Solutions of Germany, demonstrated software that could allow people to read and write to most RFID tags. Presently, RFID tags are not read-protected, and few are write protected. The vulnerability could be exploited by shoplifters.

http://www.gcn.com/cgi-bin/udt/im.display.printable?client.id=gcndaily2&story.id=26759
http://zdnet.com.com/2102-1105_2-5287912.html?tag=printthis