I have been a long-term member on two internet forum websites.  I have enough reasonable evidence to suspect that someone from one website forum followed me to the other.  I won't go into detail why or how it was done, but the point remains is that there is a high probability of my suspicions being correct.  Now, I would like to know how I can find out someone's IP address, so that I can see if the two IP addresses, one from each forum, match.  In what way would it be possible for me to find this out?  Thank you.