Ok in order to pose a question to everyone on MR, I'm going to have to suffer some embarrassment.

I have been banned from the BITOG forum for the second time.
BITOG stands for Bob Is The Oil Guy.
http://theoildrop.server101.com/cgi/ultimatebb.cgi
The first time I was banned for: Insulting Mobil 1 oil by equating it with paint thinner. The second time I was banned for: Stating that 5W-20 oil provides no long term protection without providing a reference to backup my claim. Now that you have all the boring detailes, I can move towards my question.
I was able to rejoin the forum after being banned the first time by creating an email sub account, (SBC lets you have up to 25 sub accounts), but a few days ago when I try to rejoin again by using another email sub account, my membership application was denied. So I'm thinking to myself: Hmmm, they must have gotten some kind of new software to detect me. Maybe they're able to detect my IP address, to where as before, they weren't.
Now that my curiousity has overcome my embarrassment, I'm able to pose this question: How do they know it's me?
Keep in mind that I have no intention of ever joining the forum again, (since no one over there listens to my advise anyway) I'm just curious as to why I fooled them the first time, but not the second time.