Information Security is everywhere: as the world becomes more and more digitized, so it becomes more and more hackable. Cyber attacks, data breaches, and even cyber warfare are all very real – so it’s infinitely important to understand how hackers think and act, and how you can fight back. In this course, which is the second part of the Unlocking Information Security program, you will turn your attention to the Internet: you’ll start by learning about the inherent vulnerabilities lurking in the multiple layers of the Internet’s protocol stack and then meet the first line of internet defenses. Next, you’ll take an in-depth look at the modern cryptographic concepts that are at the core of internet security and discover the mathematical miracle that makes them possible. With all this in mind, you will take a deep survey of the world wide web; understand the various technologies behind websites, how web servers and web browsers interact, how they can be attacked, and how they should be defended. Finally, you will learn about viruses, worms and trojans: what they are, how they spread, hide and attack, and the arms-race between them and the anti-virus industry. This course was produced at Tel Aviv University by TAU Online – learning innovation center.