Puntuación alta seguridad

if($_GET['sessionID'] == $user->data['session_id'])
    {
        $score = $_GET['score'];
        $username = $user->data['username_clean'];
    
        if($username != 'anonymous')
        {
            $sql = "SELECT score FROM games_batball WHERE username = '$username' ORDER BY score DESC";
            $result = mysql_query($sql);
            $row = mysql_fetch_assoc($result);
            if($row['score'] < $score)
            {
                $sql = "INSERT INTO games_batball (username, score) VALUES ('$username', '$score')";
                $result = mysql_query($sql);
                $message = 'Your Score Was Added';
            }
            else
            {
                $message = 'Your older score of '.$row['score'].' was higher.';
            }
        }
    }