[Plugin: Password Protect WordPress] Not working

I think I have found a more reliable and straightforward approach. Copy and paste this code inside your theme functions.php:

function walled_garden() {
if( ! is_user_logged_in() )
wp_redirect( '/wp-login.php' );
}
add_action( 'get_header', 'walled_garden' );

I Got it from : http://davidwalsh.name/wordpress-force-login (see the comments).
I think its far better to have a User Login approach to handle this, and avoid plugins that might, as it did happen to me, allow hack and malware contamination when it’s buggy.