When something sounds "too good to be true," that's probably because it is.

Around this time of year, you may see posts from dozens of your friends asking you to participate in the "Secret Sister Gift Exchange," which promises to be a secret-Santa style gift-giving experience, but instead of getting one gift in exchange, you could get up to 36.

But how is that mathematically possible? It isn't. In fact, this is a scam well-known by the Better Business Bureau, and is technically illegal.

Think about it this way. Let's say 100 people enter into this exchange. That's 100 \$10 gifts being sent out, right? So the first person might get 36 gifts! Wow! Then the next might get 18. Still pretty good. But that's already over half of the total number of gifts sent out, going to just two people. How will the other 98 get 6-36 gifts at that rate?

They won't.  This method of operation is also called a "Pyramid Scheme." And not only that, now you name and address have been sent out to people you don't know, who can now see all of the cute photos you post of your family on Facebook. Sounds scary now, doesn't it? That's why police are warning against this scam that has been around since late 2015.

Don't fall for the secret sister scam, instead participate in your office Secret Santa, or give gifts to children in need this year with one of the many legitimate charities set up during the Holiday season.