I used to be registered for a forum and logged in to read and post there. Obviously, that meant that the forum's admin knew my IP. Lately, however, I've been just reading that forum as a guest, i.e., without logging in. The admin recently posted that I was reading the forum. How could he possibly know that?
Thanks for your question Simon_y7.
To my knowledge, all webservers keep a log of all visitor IP's and user agents and the time of the visit. I only work with Linux/Apache based webservers and I know by default they all keep such records.
Forum software is usually even more intense at keeping track of visitors and users.