Cyanobacteria is more commonly known as "blue-green algae", and it wasn't initially put into the moneran kingdom. It had the ability to conduct photosynthesis like other algae, and was temporarily in the plant kingdom. Later scientists discovered that cyanobacteria was prokaryotic whereas regular algae is eukaryotic, and decided to slip it into the moneran kingdom because it had not contained a nucleus. Cyanobacteria has helped us a little, as it produces oxygen as a gas as a by-product of its photosynthesis. Unfortunately, this ended up leading to the near-extinction of many oxygen-intolerant organisms. It harms us in a way as well, since it is highly toxic.