Interesting paper by Steve Bellovin - Worm propagation in a v6 internet

http://www.cs.columbia.edu/~smb/papers/v6worms.pdf - courtesy Schneier on Security and then the ITU newslog.

Internet Worms and IPv6

Bruce Schneier's Schneier on Security points to a paper dismissing the myth that worms won't be able to propagate under IPv6.