Block windows users from wordpress blog

function block_windows() {
    if( preg_match( '/win/i', $_SERVER['HTTP_USER_AGENT'] ) ) {
        //echo 'windows';
        wp_die('Sorry, you need to be linux user to visit the blog');
    } else {
        //echo 'linux';
    }
}
add_action( 'init', 'block_windows' );