I have searched google for an answer to my question and can’t seem to find one. Maybe you can help me out. Is it possible to use somebody else’s IP addresses to post on a forum with? I am a moderator of a health website where we had multiple sock puppet accounts. Duplicate IP’s associated with one user came from a Comcast static broadband account, A & T mobile account, a mail server belonging to a business, and a doctors’ office. I asked the member who the IP’s were matched to what was going on. He said a friend of his who had been banned from our website had asked him to put software on his phone, his wifi, and his business that would make it look like he was posting from these addresses. That didn’t explain the use of the doctor’s office IP. Is this possible or am I being lied to? Thank you for taking the time to answer me.
(For clarity, I'll refer to the "banned user" and the "other user" in my response.)
The banned user could ask anyone, including the other user, to install software such as a proxy or a VPN that would allow him to route traffic through those computers. Such software could be installed on routers, computers, or cell phones, so all of the sources you describe are certainly possible. While I can't say for sure, it's possible that the doctor's office was visited by the other user and his phone connected to their wifi, resulting in the traffic appearing to come from that source.
IP address bans are quite fragile in this way. There are many ways for someone who knows a little bit about technology to make their traffic appear to come from any number of sources -- public proxies, VPN services, TOR relays, private proxies, compromised servers, public WiFi, among others. Beyond that, most ISPs in the US use a system (DHCP) that assigns IP addresses for only a period of time, after which the IPs may be rotated. So not only might your banned user end up with a different IP address at their home, but the IP you have banned might end up being assigned to someone else who will wonder why they have been banned from your forum.