Many people who use social media are receiving invites from friends and family to participate in a "Secret Sister" gift exchange. 

According to the website, Snopes, it unlikely those participating will receive dozens of free gifts in the mail. The following is from the Snopes article which you can read in full here: Secret Sister Gift Exchange

This gift exchange scheme started to spread online in late October 2015.  People are invited to participate in a process that involves sending one present (usually valued at $10) and receiving 36 in return. Participants who opted in to the "secret sister" exchange are instructed to send a gift to the first "sister" on the list, move the second on the list to the first spot, and put their own name into the second spot. 

The exchange sounds like a great idea but there's at least one tiny problem. The chain letter scheme could be illegal if they request money or other items of value and promise a substantial return to the participants. Chain letters are considered a form of gambling, and sending them through the mail (or delivering them in person or by computer, but mailing money to participate) violates Title 18, United States Code, Section 1302, the Postal Lottery Statute. Chain letters that are allowed can ask for items of minor value, like recipes since they are not things of value under the law.

This is how the chain letter looks: 

Welcome to our secret sister gift exchange! Here's how it works:

1) Send one gift value at least $10 to secret sister #1 below.

2) Remove secret sister's name from #1; then move secret sister #2 to that spot.

3) Add your name to #2 with your info.

4) Then send this info to 6 other ladies with the updated name info

5) Copy the secret sister request that I posted on my wall, to your own wall. If you cannot complete this within 1 week please notify me, as it isn't fair to the ladies who have participated and are waiting for their own gifts to arrive. You might want to order directly from a web-based service (Amazon, or any other online shop) which saves a trip to the post office. Soon you should receive 36 gifts! What a deal, 36 gifts for giving just one! Be sure to include some information about yourself ... some of your favorites. Seldom does anyone drop out because it's so much fun to send a gift to someone you may or may not know ... and of course it's fun to receive. You should begin receiving gifts in about 2 weeks if you get your letters out to your six people right away.