If you got a package in the mail that you didn't order, it may be a scam.

The warning comes from the Federal Trade Commission and cyber experts.

They say the mystery deliveries are known as brushing scams.

Officials say third-party sellers on Amazon, eBay and other online marketplaces pay people to write fake, positive reviews about their products.

A fake account is used to place the orders addressed to random people.

Then the brushers send a cheap, often lightweight item in place of the more expensive product being reviewed.

The FTC has gone after marketers that use fake reviews, but it's not illegal to send customers unordered merchandise.