What is the OWASP Top 10 and why does every developer need to know it?

OWASP Top 10 is the list of the 10 most critical web application security risks, updated every few years.

**2021 OWASP Top 10:**
1. Broken Access Control
2. Cryptographic Failures (sensitive data exposure)
3. Injection (SQL, NoSQL, OS command)
4. Insecure Design
5. Security Misconfiguration
6. Vulnerable & Outdated Components
7. Identification & Authentication Failures
8. Software & Data Integrity Failures
9. Security Logging & Monitoring Failures
10. Server-Side Request Forgery (SSRF)

**Why developers must know this:**
- 80% of web attacks exploit these 10 categories
- Required knowledge for PCI-DSS, ISO 27001, SOC 2 compliance
- Asked in security interviews at every company
- Using libraries like Django, Laravel, Spring reduces risk but doesn't eliminate it

Learn each one, understand the attack, then implement the defence.