Do an extra validation on the form data

css-tricks-bob-form-validation.php

<?php
//validate first name
if(strlen($form_data['first_name'])>30)
{
    die('First name too long');
}

//validate last name
if(strlen($form_data['last_name'])>30)
{
    die('Last name too long');
}

//validate email
if(!preg_match('#^[a-z]([a-z0-9]*[-_\.]?[a-z0-9]+)*@([a-z0-9]*[-_]?[a-z0-9]+)+[\.][a-z]{2,3}([\.][a-z]{2})?$#i',$form_data['email'])
{
    die('Invalid email address');
}