CommonCraft popularised the paper-and-marker pen style of video explanation, and some of their original videos are still the best. Secure Passwords Explained by CommonCraft does exactly as you might expect.

Microsoft's Password Checker and the site How Secure is my Password? offer quick ways to see how the complexity of a password significantly alters how easy it is to crack: for obvious reasons it is probably better to use these sites with imaginary passwords rather than your real passwords!

The National Codes Centre at Bletchley Park (who know a thing or two about ciphers) have comprehensive lesson plans, teacher's notes, and student activities for various types of encryption, from simple substitution ciphers (Caesar ciphers) through the infamous Enigma and Lorenz ciphers to modern day methods.

The news articles below cover some of the major risks of malicious actions such as hacking or malware. Myriad examples of these problems exist (and new ones seem to appear every few weeks), but the examples below highlight some of the more famous cases (and the greatest losses).

• Target Expects $148 Million Loss from Data Breach
• Security lapses at Apple and Amazon lead to an epic hack
• McDonald’s customers’ data exposed in a Big Mac hack attack
• Sony fined over 'preventable' PlayStation data hack
• Lost in the post - 25 million at risk after data discs go missing
• Zurich Insurance fined £2.3m over customers' data loss
• Doorstep lender Shopacheck fined £150,000 for data loss
• Home Depot: Card breach put 56M cards at risk

Very detailed but clear explanations of the various types of encryption systems, from simple substitution ciphers (Caesar ciphers) to modern public key encryption systems. The page also explains the types of attacks that can be performed against ciphers, such as known plaintext attacks and frequency analysis attacks. A variety of interactive applets held improve understanding.

The news articles below cover some examples of (in)famous errors in databases, from relatively minor to major errors in voting systems.

• French phone bill waived after 12qn-euro blunder
• Meet Mikey, 8: U.S. Has Him on Watch List
• Dead girl given truancy warning
• Outrage at 500,000 DNA database mistakes
• Florida’s flawed “voter-cleansing” program

The card flip 'magic' game is a great idea from Computer Science Unplugged. The teacher sets up a grid of black/white cards and asks students to turn over one card without the teacher seeing. Using parity rules, the teacher is able to 'magically' determine which card the students turned over. This is a really fun game which demonstrates how simple techniques like odd/even partity can be used to solve significant problems.

The Computer Science Unplugged page has a range of support material: instructions for teachers, videos of the activity being performed, and a PDF download with extension activities and details about check digits in ISBNs.

This interactive online game is like a digital version of the parity card game. Students are presented with an 8x8 grid. They must first set the parity bits correctly using even parity. The computer will then scramble the grid and change a single bit, which students must identify using the rules of parity.