Restrict number of user account sign-ups in a period?

Question

I have a web app that requires a user to have an account. This user can then vote 'once' on a specific item. However, some users are signing up for lots of accounts to 'game' the system.

Does anyone have any ideas how you can restrict this type of thing?

Could I restrict number of signups per day per IP address? (what are problems with this?)

Any other suggestions???

Answer 1

You would do yourself one better by restricting the sign-ups to just a single IP address per user. This may not be good if you plan on having families all living under the same roof to have their own accounts, but in most cases this is practical.

Answer 2

Yes, restricting signups per IP is reasonable. I'd probably go with signups per rolling time period (say, a maximum of one new account in any one-hour period per IP). You might also flag suspicious signups (say, more than five per day per IP) for later followup.

You might also restrict users from voting until they've passed some hurdle, similar to SO's reputation system. Prevent poll voting until they've been a user for a week, have posted at least twice, have one friend request, etc.