Re: Welcome back … (updated)
Its basically when u are using somone else’s IP to surf on internet. Like I have setup my own proxy script here (can also mange cookies etc), its base64 encrypted 
otherwise there are thousand of other sites who offer proxy and anonymous surfing, also some proxy plugins can be applied on firefox so far i know.
But I am pretty sure, those who have posted porn etc, were probably dum enuff to use their real internet ip.