I've been on forums where banned people would sneak back in by using a computer at a public library, where the ISP# wasn't banned. It's silly, but it somebody's determined to make an ass of themselves, they usually find a way.
It is easier than that. All you need to do is go to a website which allows you to run through their server which assigns you an IP anywhere in the country. I remember pointing this out on the PNJ, and the PNJ erased my post, like all the socks had not already figured it out. I always find it curious how two forum members can have conversations with themselves which are perfectly spaced and timed. Now if that person is using two browsers like explorer and chrome, and has set up separate ips for each of those browsers, they can carry on a conversation with themselves. I will give a hint that we have socks here who never post at the same time over the last two years, while others routinely post while another is posting. Of course, once being given my warning, our socks will use two computers and send at the same time to try to prove they are not socks, but heck......there is two years of evidence without one simultaneous post. I really think there is an intelligent threshold with socks. We have some very good ones, and we have some folks who are not as smart as the best socks.