Holiday shoppers, beware — that gift left sitting on your porch all day might be gone by the time you make it home. Have you ever heard of "Porch Pirates"? They run rampant during the holiday season, sneaking up on unsuspecting homeowners and stealing packages left on the front porch, according to CNBC. It's a phenomenon that is becoming a common occurrence, and many local law enforcement officials are warning people who do online shopping to be careful.

The National Retail Federation believes that this year, nearly half of all shopping will be done online, and consumers need to be wary, according to CBS News. Data taken from insuranceQuotes.com shows that an estimated 23 million Americans will have packages stolen before they are even able to open them, according to CNBC. This becomes an even bigger problem during the holiday season.

"Porch Pirates" will follow a delivery driver to a destination, wait until they drop off a package, and steal that package before the owner ever realizes it has arrived, according to NBC News.

Customers like Rick Deckman are trying to fight these instances, setting up cameras and catching thieves in action. "I was blown away. I mean, I just couldn't believe that something like this was really happening," he said, according to NBC News.

Delivery services and retailers are trying to fight back against these crimes, requiring homeowner signatures, starting package alerts and allowing customized drop-off points for deliveries, according to CNBC.