need to modify this script

I was using this piece of php code for a site.
Now its old and I recently had a few attacks. Script was used for to include another file from someplace else and send spam. Obviously this makes my script as spam sender.

for the content

$htm = ".htm";
$pid = "$details$htm";
function show_details($pid)
{
if (!preg_match("/http/", $pid)) {
require($pid);
} else {
   die;
}
}

PHP:

and for the title, desc , keywords etc..

$txt = ".txt";
$title = "$details$txt";
function show_title($title)
{
if (!preg_match("/http/", $title)) {
if (file_exists($title)) {
require($title);
} else {
   die;
}
}
}

PHP:

and a display.php file with

print '
<!-- CONTENT -->
';
show_details("$pid");
print '

PHP:

by this code ı was able to call any content by "/display.php?details=mycontentpage"

mycontentpage.htm
mycontentpage.txt



.............


Now this code has to be re-coded .. I can not change the construction as the site is just too big.
So I guess I just have to stick to this..

Can anyone help ? Any comments ?

 

if ( !preg_match('/[^A-Za-z0-9]/', $string ) )
{
	// safe file name
} else {
	die('BAD FILE NAME');
}

PHP:

if you want to you - and _ chars , you must use this

if ( !preg_match('/[^A-Za-z0-9-_]/', $title ) )
{
	// safe file name
} else {
	die('BAD FILE NAME');
}

PHP:

 

:S it does not work..
I would prefer something with domain name or a host solution.

Any suggestions ?