Not necessarily a hack, it's more likely that he hasn't updated/reverted some templates.
Revert the search template for one, and navbar if you haven't modded it. If you do have a custom navbar template, you'll need to add:
Code:
<input type="hidden" name="securitytoken" value="$bbuserinfo[securitytoken]" />
Right underneath:
Code:
<input type="hidden" name="do" value="process" />