That's a contract between users and HN. Airtrain is a 3rd-party. If HN API exposes personal information publicly through their API then there is a problem. An

That's a contract between users and HN. Airtrain is a 3rd-party. If HN API exposes personal information publicly through their API then there is a problem. And AFAICT the only way for HN to prevent user comments from being used by 3rd-party is preventing access to those comments, meaning a) sign-up will have to be more stringent and b) visitors will have to sign-in just to read (or scrape) comments.