Control via php

Hi all,
i'm using the ShareThis module and it's a very good project.
My problem is that i need to control via php showing or not share icons.
I need that because i've private content (various types of content, same of public content), and i don't want sharethis to appear on that private content.

I mean, i need to insert somewhere an

<?php
if ($node -> term == 'something') {
 print render($content['sharethis']);
}
?>

or something else somewhere.
I know this code is incorrect, it's just an idea.
How can I achieve this?
Thanks in advance.
Edubacco