Some routers switch IP's frequently, and ISP's switch user IP's on a consistent basis. The major flaw in this is that after the one jerk gets banned, someone else takes all the crap. I've been banned in online games before and all I had to do was go into the command prompt and type in "ipconfig /release" then "ipconfig /renew" and I was already on a new ip. The only way to totally block a person would be through program cd keys, but it's not very wise to be releasing this.