Form validation

Hello ,

I'm doing a form validation in codeigniter like the following : 
$this->form_validation->set_rules('first_name', 'First Name', 'trim|xss_clean|required');

if insert in my field the word "<script>" , the xss_clean is removing the word "<script>" and the field becomes empty and the required validation is bypassed and accepting the empty entry and it can be inserted in my database.

could you please help me with this .
Thanks