Links

An animation movie about bot networks by the Dutch Government Computer Emergency Response Team (65 MB WMV file):
http://www.bsi-fuer-buerger.de/abzocker/bot_netze.htm

Webpage to the book "The Code Book" by Simon Singh from the year 2000 and the corresponding Cipher Challenge:
http://www.simonsingh.net/The_Black_Chamber/home.html

Website of the Cryptoclub of the University of Illinois at Chicago (UIC):
http://www.cryptoclub.math.uic.edu/indexmain.html
(very colourful, for kids, Macromedia Flash required)

NSA site for kids:
http://www.nsa.gov/kids/

Website on the National Cipher Challenge NCC (University of Southampton, IBM, GCHQ):
http://www.cipher.maths.soton.ac.uk

Secret Codes and the Enigma Machine (for pupils, site a little bit outdated):
http://motivate.maths.org/conferences/conf95/c95_resources.shtml