public static function valid($filename = null)
	{
		if (!$filename)
		{
			return false;
		}

		if (preg_match("/^\s*http[s]{0,1}:/i", $filename))
		{
			return false;
		}
		if (preg_match("/^\s*[\/]{0,1}index.php\?/i", $filename))
		{
			return false;
		}
		// Disallow windows drive letter
		if (preg_match("/^\s*[.]:/", $filename))
		{
			return false;
		}
		// Disallow \
		if (strpos($filename, '\\'))
		{
			return false;
		}
		// Disallow ..
		if (strpos($filename, '..'))
		{
			return false;
		}

		return true;
	}