Oh I see, it protects pages from public view. I thought for a second you were trying to prevent others from using PHP to scrape content from your site or something.
As far as the input, the input itself isn't being used inside a query so it really isn't too bad. There isn't much that a person could do maliciously. Might want to strip_tags, trim (for whitespace) and possibly toss htmlspecialchars against it (if you print the supplied input to browser you will want to). You may also want to use get_magic_quotes_gpc to check magic quotes setting and addslashes or stripslashes from there.
I just installed Ubuntu due to virus' on the Windows disc I downloaded, but I will download again and scan over everything.