Security
Introduction
Use technology securely
Self study resources
Schneier on Security - leading US blog on a wide range of information security issues.
A number of school network firewalls include https / ssl decryption as standard.
Resources for lectures or group study
Excellent resources on safety and security as part of Google's Good to Know campaign in association with CAB.
Resources for use with pupils
Passwords Circle Time Activity
GCHQ sponsors the Cyber Security Challenge and Southampton's National Cipher Challenge. See also online cryptography resources for children from the NSA (US)
Lovely collection of interactive cryptography resources from Simon Singh
Rather nice new website for Bletchley Park, which is a great place for a school trip. See also The National Museum of Computing, also at Bletchley Park.