How to Tell if a User has a Fake Account?

Same IP, but could it be other family members?

[asas111]

Our forum has a policy where a user can't have more than one user name. This is to prevent users from creating fake accounts, or to avoid having a user still posting under a fake name, even after his first user name was banned.

Some users have registered a second even a third name, and I could tell it was them based on IP number.

I confronted some of them, and told them about it, and they came back to tell me that 'it wasn't them, but someone in the family' and I usually have my doubt about this, even though it is almost impossible for me to prove. So my question to you guys is:

-How can I tell if a new username, whose IP matches that of an existing user, is the same user, or maybe someone else in the family?

Thank You

[rogerd]

Sometimes there are valid reasons to register more than once. Obviously, some people do share the same IP or PC. Sometimes, a long-time member may want to ask a personal question or post on a controversial topic without being identified.

It's a judgment call, but I'd recommend focusing on behavior. If a previously banned member returns and is behaving admirably, why worry about it? On the other hand, when multiple IDs of the same person are posting in the same thread and supporting each other's position, then it's time to bring the hammer down. Rather than trying to stamp out every multiple, just nail those that are causing problems.

[bouncybunny]

One, or maybe two, members of a family might be interested in the same subject enough to become members of an online forum. But three?

Depending on the subject matter of the forum I would put this as ranging from unlikely to, 'pull the other one'. ;)

[rogerd]

Of course, people share IPs in offices, schools, college dorms, coffee shops, etc.

vBulletin has a hack that places a non-obvious cookie on the user's computer. It then tests for this and alerts mods if multiple members are posting from the same machine. This is a good addition to IP checking, as it proves sharing at the machine level (important for AOL users, for example, where IPs are useless) and also catches those who may move a laptop to different locations to evade detection.

[maximillianos]

I wouldn't worry so much about folks having multiple accounts... focus more on why they have multiple accounts. Perhaps they lost their password and just re-registered. Perhaps more than one person in the household, etc. What you need to watch is what they are doing. If they are using multiple ids to game your site... then you have a problem... and they should be banned.