Cyber security is the practice of protecting information and the systems that handle it from harm. This lab is entirely about defence: how to notice problems, how to reduce them and how to recover. You will not find attack recipes here, and the threats you meet are shown as shapes and signals, never as instructions.

Every company, person, e-mail address and web address in this lab is invented. Addresses ending in .example or .test and the number blocks 192.0.2.x, 198.51.100.x and 203.0.113.x are reserved for documentation, so they never point at a real place.

Before we can defend anything, we need to say what "protected" means. Security people use three words, known as the CIA triad (nothing to do with any agency):

• Confidentiality: only the people who are allowed to see the information can see it.
• Integrity: the information has not been changed by someone who should not change it, and you can tell if it has.
• Availability: the system and the information work when the right people need them.