Security Fundamentals

Three practical rules that prevent most common vulnerabilities:

• Never build a SQL query by joining strings together with user input — always use parameterized queries (the ? placeholder from the Databases lesson).
• Never trust data from a user or an external API without validating it first — check the type and range of values before using them.
• Never commit secrets (API keys, passwords) to version control — load them from environment variables instead.

Security is mostly about consistently applying a small number of habits like these, not one clever trick.