computer science / security
Learn Computer Security for Free
Learn to think like an attacker so you can defend like a pro. From university systems-security courses to hands-on hacking labs you can legally play in — the best free ways to learn the foundations of cybersecurity.
Computer security is a mindset before it's a skill: assume everything can be attacked, then find out how. This page focuses on the computer-science foundations of security — how systems and web apps are actually broken and defended — through university courses and legal hands-on labs. The fastest way to learn is a mix of theory (why systems break) and practice in safe, purpose-built environments that want to be hacked. The one unbreakable rule: never practice on systems you don't own or aren't authorized to test — that's the line between learning and a crime, and the labs below exist precisely so you never have to cross it. This guide covers the free courses, the practice platforms, and how to learn security responsibly.
01 · FUNDAMENTALS
Security fundamentals
University-grade courses on how systems, networks, and web apps are attacked and defended.
- MIT 6.858 — Computer Systems Security ↗MIT's respected systems-security course, with free lecture videos, notes, and labs on real vulnerabilities.css.csail.mit.edu
- OWASP Top 10 ↗The essential free reference for the most critical web-app security risks — the vocabulary every security learner needs.owasp.org
02 · HANDS-ON LABS
Practice hacking (legally)
Safe, purpose-built environments to actually break things and learn by doing.
- PortSwigger Web Security Academy ↗The best free, hands-on web-security training anywhere — interactive labs from the makers of Burp Suite.portswigger.net
- TryHackMe ↗Guided, gamified cybersecurity training with a generous free tier — beginner-friendly rooms that teach by doing.tryhackme.com
- picoCTF ↗Carnegie Mellon's free capture-the-flag platform — learn hacking through fun, self-paced challenges.picoctf.org
03 · HOW TO LEARN IT
How to approach learning security
Security rests on other CS knowledge, so the strongest learners build the base first: how computers and networks work before how they're broken. You can't exploit or defend a system you don't understand. Pair one structured course (like MIT 6.858, or the OWASP Top 10 for web) with steady hands-on practice on the legal labs — theory plus doing is the combination that sticks. Then pick a direction: web security, systems security, or network security each go deep.
04 · THE LEGAL LINE
The one rule you can't break
This matters enough to state on its own, because getting it wrong can end a career before it starts:
05 · FAQ
Frequently asked questions
Where should I start learning computer security?
Start with the fundamentals of how systems and the web work, then learn common vulnerabilities using the OWASP Top 10 and a university course like MIT 6.858. Pair that theory with hands-on practice on legal platforms such as TryHackMe and the PortSwigger Web Security Academy.
Can I learn ethical hacking for free and legally?
Yes. Platforms like TryHackMe, the PortSwigger Web Security Academy, and picoCTF provide free, deliberately vulnerable targets that are legal to attack. They are built specifically for practice, so you can learn real offensive skills without any legal risk.
Do I need a CS degree to work in security?
No. Many security professionals are self-taught or come from IT and development backgrounds. Employers value demonstrable skills, hands-on lab experience, and relevant certifications, all of which you can build with free resources and consistent practice.
What should I learn before cybersecurity?
Understand networking and how the internet works, get comfortable with the Linux command line, and know how operating systems and web applications function. This foundation makes security concepts and hands-on hacking make sense rather than being commands you copy blindly.
Is it illegal to practice hacking?
Practicing on systems you own or are explicitly authorized to test, including purpose-built labs, is completely legal. Attacking systems without permission is illegal even if you cause no harm, which is why you should keep all practice on legal platforms and your own machines.