25 reputation and -10% downvote accounts

I do not understand what is the story of accounts with 25 reputation which downvote on regular basis my posts with -10% of power?

Is this happening to you too?

None of them has never posted or commented on anything, as if their only purpose is to press downvote button :)
But I don't understand it either, because they don't do much harm, with 10% of almost nothing does not affect much the overall payout or I'm wrong?

Thanks in advance for the answers,I don't think i'm the only one who's going on with this phenomenon and that the community will be interested to hear the story:)