What is the best way to protect my DB class from being hacked [closed]
class dbinterface {

    private $_dbLink;
private $dbHost = 'host';
    private $dbUser = 'user';
    private $dbName = 'name';
    private $dbPass = 'pass';
    private $dbUserTable = 'table';

 public function connect ()
{
    $this->_dbLink = mysql_connect($this->_dbHost, $this->_dbUser, $this->_dbPass);
    if(!$this->_dbLink)
        throw new Exception ("Could not connect to database. " . mysql_error());
}

function registerUser($userName, $userPassword) {

    $db = new db();
    $db->connect();

    // Select database
    mysql_select_db($this->dbName);

    $query = "insert into usersExample values (NULL, "$userName", "$userPassword")";
    $result = mysql_query($query);

    // Test to make sure query worked
    if(!$result) die("Query didn't work. " . mysql_error());

    // Get the user ID
    $this->userID = mysql_insert_id();

    // Close database connection
    mysql_close($dbLink);

} // End registerUser()

<?php defined('IN_APP') or die('No access allowed.');

define('IN_APP', true);