Security failures are rarely exotic; most come from skipping basic hygiene. SQL injection happens when user input is inserted directly into a database query without proper handling, letting an attacker manipulate the query itself, for example typing input that tricks the database into returning all records instead of one. Cross-site scripting (XSS) happens when untrusted user input is rendered on a page without sanitization, letting an attacker run their own script in another user's browser. You will learn why passwords must always be hashed (irreversibly scrambled with a one-way function) rather than stored as plain text, so that even a data breach doesn't expose users' actual passwords, and the habit of validating and sanitizing every piece of user input, since input is the most common attack surface in any application.