I seem to have acquired a secret admirer who systematically downvotes my answers for a while now. Almost every day I get downvotes on various old answers, sometimes several in a row. Never more than 5 (limit for daily downvotes), which means the same person is doing it. Never a comment is left (which by itself is rude, IMHO, and I don't understand why SE allow downvotes without comments).
Is there any mechanism to identify such manipulations and eliminate them/block the offenders? It kindof defeats the purpose of showing the visitors what answers are considered as good by the community.