What best practices should PHP developers follow when handling user-generated content, such as comments or guestbook entries, to mitigate potential security threats?

When handling user-generated content in PHP, developers should sanitize and validate input data to prevent SQL injection, cross-site scripting (XSS), and other security vulnerabilities. It is important to use prepared statements for database queries, escape output data, and implement input validation to ensure that only safe and expected data is processed.

// Example code snippet for sanitizing user input in PHP
$userInput = $_POST['user_input'];

// Sanitize user input to prevent SQL injection
$cleanInput = mysqli_real_escape_string($connection, $userInput);

// Validate user input to prevent XSS attacks
$cleanInput = htmlspecialchars($cleanInput);

// Use prepared statements for database queries
$stmt = $connection->prepare("INSERT INTO comments (content) VALUES (?)");
$stmt->bind_param("s", $cleanInput);
$stmt->execute();
$stmt->close();