Free course on Professor Messer
Professor Messer's free CompTIA Security+ (SY0-701) course consists of 121 videos totaling roughly 15 hours, covering every exam objective: threats, identity and access, cryptography, network defense, and incident response. If you're planning to take the Security+ certification exam, this is the de facto industry-standard free study resource used by thousands. It's designed for IT professionals or students with networking knowledge already (Network+ level) pursuing the Security+ credential. The limitation: it is exam-prep-shaped and focuses on passing the test rather than building hands-on labs. The exam itself costs money.
CybersecurityBeginner
Harvard's introduction to cybersecurity for technical and non-technical audiences. Covers threats, authentication, networking, system security, and operational security. Free to audit; certificate available via edX.
CybersecurityBeginner
TryHackMe's free Pre-Security learning path. Covers cybersecurity careers, basic networking, web fundamentals, Linux, and Windows. Designed for total beginners with no IT background.
CybersecurityBeginner
TryHackMe's flagship beginner path covering the breadth of cybersecurity: networking, web exploitation, cryptography, defensive security, and incident response. Mostly free with hands-on rooms.