What are some common vulnerabilities that Spambots exploit on websites developed with PHP?

One common vulnerability that Spambots exploit on PHP websites is inadequate input validation, allowing them to inject malicious code or spam content into forms or comments. To prevent this, developers should always sanitize and validate user input before processing it.

// Example of sanitizing user input in PHP
$input = $_POST['user_input'];
$clean_input = filter_var($input, FILTER_SANITIZE_STRING);