Решил проблему дополнительной проверкой на содержание в сообщении ссылок:
includes/product_detailed.php
строчка
//validate input data
if (trim($customer_email)!="" && trim($customer_name)!="" && trim($message_subject)!="" && trim($message_text)!="" && eregi("^[_\.0-9a-zA-Z-]+@([0-9a-zA-Z][0-9a-zA-Z-]+\.)+[a-zA-Z]{2,6}$", $customer_email))
меняется на
//validate input data
if (trim($customer_email)!="" && trim($customer_name)!="" && trim($message_subject)!="" && trim($message_text)!="" && eregi("^[_\.0-9a-zA-Z-]+@([0-9a-zA-Z][0-9a-zA-Z-]+\.)+[a-zA-Z]{2,6}$", $customer_email)&& !preg_match ("/href|url|http|www|\.ru|\.com|\.net|\.info|\.org/i", $message_text))
includes/product_detailed.php
строчка
//validate input data
if (trim($customer_email)!="" && trim($customer_name)!="" && trim($message_subject)!="" && trim($message_text)!="" && eregi("^[_\.0-9a-zA-Z-]+@([0-9a-zA-Z][0-9a-zA-Z-]+\.)+[a-zA-Z]{2,6}$", $customer_email))
меняется на
//validate input data
if (trim($customer_email)!="" && trim($customer_name)!="" && trim($message_subject)!="" && trim($message_text)!="" && eregi("^[_\.0-9a-zA-Z-]+@([0-9a-zA-Z][0-9a-zA-Z-]+\.)+[a-zA-Z]{2,6}$", $customer_email)&& !preg_match ("/href|url|http|www|\.ru|\.com|\.net|\.info|\.org/i", $message_text))