Safety on 404 error doc - php

Question

I am working on my 404 error doc, and I was thinking instead of just giving a sitemap, one could suggest to the user the website he might have looked for based on what actually exists on the server.
Example: if the person typed in "www.example.com/foldr/site.html", the 404 page could output:
Did you mean "www.example.com/folder/site.html"?
For this, I wrote the following code which works for me very well. My question now is: is it "safe" to use this? As basically someone could detect all files on the server by trying all kind of combinations. Or a hacker could even use a script that loops through and lists all types of valid URLs.
Should I limit the directories this script can detect and propose? With an array of "OK"-locations, or by file type?
Had anyone else already got an idea like this?
PHP:
// get incorrect URL that was entered
$script = explode("/",$_SERVER['SCRIPT_NAME']);
$query = $_SERVER['QUERY_STRING'];
// create vars
$match = array();
$matched = "../";
// loop through the given URL folder by folder to find the suggested location
foreach ($script as $dir) {
if (!$dir) {
continue;
}
if ($handle = opendir($matched)) {
while (false !== ($entry = readdir($handle))) {
if ($entry != "." && $entry != "..") {
similar_text($dir, $entry, $perc);
if ($perc > 80) {
$match[$entry] = $perc;
}
}
}
closedir($handle);
if ($match) {
arsort($match);
reset($match);
$matched .= key($match)."/";
} else {
$matched = false;
break;
}
$match = array();
}
}
// trim and echo the result that had the highest match
$matched = trim(ltrim(rtrim($matched,"/"),"."));
echo "proposed URL: ".$_SERVER["SERVER_NAME"].$matched;

Answer 1

Yup, you can see it as this:
Imagine a house with only glass walls on the outside, but it's night. You're a thief (hacker) and you want to check the house for worthfull loot (files with passwords, db connections etc).
If you don't protect (certain) files, you would be putting the lights on in every part of the house. The thief would look through the windows and see that you have loot - now the only the he would have to do is get in and take it.
If you do protect the files, the thief won't even be able to know that there was any loot in the house, and thus would the thief have a higher chance of moving on to the next house.