The gullible and unsuspecting, and obviously it's worked, or it wouldn't be used. While many know better, many do not also. Don't even participate if you're able to avoid it by letting your phone ring clear through with no answer at all. These clowns may not trick you out of money, personal or financial info, or hijack your computer, but getting any kind of answer from the numbers they call keeps it from being a total loss on their part. Without numbers that have an answer, these thieves are out of luck.