When I started learning PHP, I thought security was something "advanced" developers worried about. I was wrong.

Here are 5 mistakes I made in my first projects that almost got my clients hacked. If you're a PHP beginner in 2026, avoid these:

1. Trusting User Input - The #1 Sin ❌

Mistake: Using $_GET or $_POST directly in SQL queries.

$id = $_GET['id'];

mysql_query("SELECT * FROM users WHERE id = $id");

Why it's deadly: A hacker can type 1; DROP TABLE users-- in the URL and delete your whole database. This is called SQL Injection.

Fix in 2026: Always use Prepared Statements with PDO.

$stmt = $pdo->prepare("SELECT * FROM users WHERE id = ?");

$stmt->execute([$id]);

2. Storing Passwords as Plain Text ❌

Mistake: Saving passwords directly like password123 in the database.

Why it's deadly: If your database leaks, every user's password is exposed. Hackers will try that password on Gmail, Facebook, everything.

Fix in 2026: Use password_hash() and password_verify() .…