While HN has some measures to reduce hivemind voting, it's quite rampant on the default subreddits.
I've actually changed the topcolor to #222222 in my settings so I don't see what my account's karma is. It completely ruins the ability to see the "new" "threads" etc links without a truly irritating amount of eyestrain but it's worth it - I recently asked genuine question about something I wanted clarification on and the comment ended up being downvoted to -4. Now I can't see my karma score I don't care about this, whereas before when my karma was shown on almost every single page throughout the site I'd obsess over making my comments universally good.
Comments are manipulated by teams of paid "trolls", including in English, and including Hacker News (when the article is of interest to a particular corp or gov -- like the Tesla mass firing article on Hacker News recently, just to give an example I know of).