Police are warning online shoppers about so-called porch pirates -- people who steal shipped packages from outside houses once they're delivered.

Local police departments say they see a spike in such crimes during the holiday season.

They say that the pirates often follow delivery drivers, see where they drop off packages and then grab the boxes if no one brings them inside immediately.

To protect themselves, police say online shoppers should have items delivered to where they'll be during the day, like to their jobs. Or to a trusted neighbor's home if the neighbor is always home.

Another means of protection is to require a signature on all deliveries.

With UPS or the Postal Service, shoppers can also specify where deliveries will be left, like at a side or back door instead of a highly visible front porch. They also offer notifications for when packages are dropped off.

Amazon purchases represent a huge number of online purchases in the United States, and the company offers the option of having them delivered to local Amazon Lockers.