I have the code below in mainfile.php, is this what you are refering to?

define('XOOPS_CHECK_PATH', 0);
// Protect against external scripts execution if safe mode is not enabled
if ( XOOPS_CHECK_PATH && !@ini_get('safe_mode') ) {
if ( function_exists('debug_backtrace') ) {
$xoopsScriptPath = debug_backtrace();
if ( !count($xoopsScriptPath) ) {
die("XOOPS path check: this file cannot be requested directly");
}
$xoopsScriptPath = $xoopsScriptPath[0]['file'];
} else {
$xoopsScriptPath = isset($_SERVER['PATH_TRANSLATED']) ? $_SERVER['PATH_TRANSLATED'] : $_SERVER['SCRIPT_FILENAME'];
}
if ( DIRECTORY_SEPARATOR != '/' ) {
// IIS6 may double the \ chars
$xoopsScriptPath = str_replace( strpos( $xoopsScriptPath, '\\\\', 2 ) ? '\\\\' : DIRECTORY_SEPARATOR, '/', $xoopsScriptPath);
}
if ( strcasecmp( substr($xoopsScriptPath, 0, strlen(XOOPS_ROOT_PATH)), str_replace( DIRECTORY_SEPARATOR, '/', XOOPS_ROOT_PATH)) ) {
exit("XOOPS path check: Script is not inside XOOPS_ROOT_PATH and cannot run.");
}
}