Prevent users from starting multiple accounts?

Question

I know that in the end it, can\'t be done.

But, what are the options to:

  a) limit the options for persons to create multiple accounts,
  b)

Answer 1

One common option is to verify the persons identity through their e-mail. Actually make them respond to an e-mail sent to their account. Some sites take this a step further and don't allow addresses from domains such as yahoo, g-mail, hotmail, etc ...