How do sites like fab prevent abuse?

Discussion in 'Membership Sites' started by axion, Nov 21, 2011.

  1. axion

    axion Newbie

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    Shoppingclubs like fab often offer their members a bonus for inviting friends to the site.

    When 10 people register to fab , you get 30$ worth credits, which you can spend on the site. The invited people don't have to buy anything.

    How can they prevent people to write a script or register manually with multiple accounts just to get the money?

    They don't use captchas. Is there anything else besides IP and Cookies scan?