How can developers prevent security vulnerabilities in PHP-based websites?

Developers can prevent security vulnerabilities in PHP-based websites by using secure coding practices, such as input validation, output encoding, and parameterized queries to prevent SQL injection attacks. Additionally, keeping PHP and its libraries up-to-date, using HTTPS to encrypt data transmission, and implementing proper access controls can also help mitigate security risks.

// Example of input validation to prevent SQL injection
$user_input = $_POST['user_input'];
$clean_input = mysqli_real_escape_string($connection, $user_input);
$query = "SELECT * FROM users WHERE username = '$clean_input'";
$result = mysqli_query($connection, $query);