It depends...if one knows the IPs of a group where a 'name' is connected, like in Mudcat, it ought to be reasonably easy to sort out one from another. That does NOT means knowing your street address or real name. That info would be available only from your ISP, usually with a good cause..(i.e. a court order) The IP does 'usually' give an indication of wher in general you are...country, city.

Someone from Miami, calling themselves Rumplestiltskin, could be reasonably anonymous in a forum such as this....that is, no one could drive up to your door.