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I own a site and I banned one of my users. His I.P was 68.111.xxx.xx Later, about 2 hours later, a new user registered. Looked suspicious, and I checked his I.P which was 68.191.xxx.xx

My question is, how can I essentially know if this is the same person, putting aside intuition?

So I used whatsmyip site and looked up both I.Ps. Both are from the US, but different places and providers. So he's not the same person? Or can there be other factors?

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It's easy to use a proxy to mask your true IP address. Additionally ISPs commonly change IP addresses of users during the same session. With the IP6 transition slowly getting started that's only going to become more common.

Unfortunately there is no way to know for sure unless they do something stupid like use a common name, same/similar email address, exact same IP, etc. In cases like this your gut feeling os often times going to be better then hard evidence.

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