White bug type things on my chilli plant

I've got these tiny white things on the underside of one of my chilli plants, they're about the size of a pin head maybe a little bigger & on some of them was a little bug type creature with little legs sticking out. I'm guessing they're not going to be beneficial to the plant so i picked them off & destroyed them.

Anyone have an idea what they might be & how i can treat/prevent them from coming back?