I know I have always had them, In my early tanks I cared because the state freaked me out. I believe I have a proper bristle worm trap somewhere, If I find it it's yours. After reading up on them I have no reason to get ride of mine, just another member of my CUC. I have gotten used to them, but I don't have moonlights on the new tank yet..., and I have found a diverse CUC is the best kind.
Just make user you want them gone for the right resones. I think that they are just part of the hobby, so I recommend to do as I did and learn to love them, if you don't you will spend the life of the hobie fighting them. They come in on frags all the time.