Corrected Version:
<?php
if (!defined("WHMCS"))
die("This file cannot be accessed directly");
function userdata_field_matches($fieldname,$value,$all_vars) {
return (array_key_exists($fieldname,$all_vars) && preg_match("/$value/",$all_vars[$fieldname]));
}
function block_fuli8_tk($vars) {
if (userdata_field_matches("email", "@qq\.com", $vars)) return "Error: Userdata validation error";
if (userdata_field_matches("lastname", "fuli8\.tk", $vars)) return "Error: Userdata validation error";
if (userdata_field_matches("firstname", "5666Q\.COM", $vars)) return "Error: Userdata validation error";
}
add_hook("ClientDetailsValidation",1,"block_fuli8_tk");
?>