I am not sure this applies to this.. but on a forum I was a member of.. I suspected someone of having multipul ID's.. and ran a bunch of IP nubmers.. and found that like 25 out of 100 members all had the same IP number! OMG.. I was shocked to find out that all these people were the same person!
I called AOL, and found out that they use the same neighborhood IP or something like that, and every AOL user would have one of only a few IPs. I signed up for the trial of AOL, and posted on my old forum, and sure enough, I had the same IP as the other 25 people did.
I am not sure how all that works, but also found out about "hidden proxys".. and it pretty much told me that if someone wanted in bad enough, they could do it. I am no scientist.. and not even all that skilled with computer stuff.. but knew there was a way, and found it. So if I could do it, there are loads of others who are doing it.
I signed on to my old forum as three different people, and even on high alert, they never knew I was one and the same.. good for the user.. bad for the admin.. 