If u r using a land line or cell dongle, it's possible to trace the user (identity unknown: who is behind the PC). The time went online (log in to your ISP ie dialup your service/ISP) and log off by triangulating the signal ie your IP add (main)--ctry, secondary IP add (the exchange box or transponder in your area ---state, county), third area IP---exactly where u r (the time of logging on and off will) prove this is the user. All need these stuffs will need court warrants.
Everywhere we visited is logged with our ISP server so u visited yahoo.com at 12pm it is there on your ISP log except no one checks until a complain
is filed and checked.
From the ISP they need to get the name of the person. Of course, if u r nobody who cares. But from my own experience, my country through a Ministry banned me from going to a forum. I still got through a proxy server. I know as I am only one using this forum. The Ministry blanket banned or blocked the DNS but forgot about proxy server. The frontpage said you r banned. Surprised I tried to log in only to be blocked from logging in so I used a proxy server and successfully logged in. I was not banned by the forum admin but by my own country. They tried to trick me by posting u r banned when they r actively blocking me from the forum.
That is what I got from my security courses.