A pair of brown leather boots was snatched last week from a doorstep in the suburbs of Chicago. A computer disappeared from a front porch in Fort Worth, Texas, last month, and an iPad case was stolen outside a Long Island, N.Y., home this week.

As the peak of the holiday gift-buying season approaches and more people are ordering online, here is the downside: Grinch-like bandits are swiping the deliveries from doorsteps when families are not home. Some thieves follow UPS and FedEx trucks along their routes and nab the gifts, while others simply drive through residential neighborhoods looking for packages.

In River Forest, Ill., where the police arrested two young men last week, accusing them of stealing deliveries from homes, plainclothes police officers trail UPS trucks to ferret out thieves who might be following them, Cmdr. Jim O’Shea said.

"This is common at this time of year," O’Shea said. "We’re trying to take a proactive approach to curtail this."

So far this holiday season, Americans have spent $21.4 billion online, up 14 percent from last year, according to comScore, a research company. UPS alone expects to deliver more than 500 million packages, and with many of them being left on doorsteps, there could be more opportunities for thieves to strike.

The Better Business Bureau recommends that customers be proactive, asking their shipping companies for tracking numbers and requiring signatures upon delivery. If they are not going to be home, customers should ask for their packages to be held at a lobby desk or at a local shipping center, advised Claire Rosenzweig, the president of the group’s New York chapter.

There are no national statistics on doorstep thefts, but reports of local episodes abound. In Burbank, Calif., with five reported incidents this year, compared with one last year, two teenagers were picked up last month after they were found trailing a UPS truck. One juvenile was released, while the other person, Ararat Gevondyan, 19, was arrested.

"It’s a crime of opportunity," Sgt. Darin Ryburn of the Burbank Police Department said. The burglars are "going through these packages for items that could be resold," he said.

On Long Island, two young men were arrested this week, suspected of stealing headphones, an iPad case and two pairs of Skechers shoes.

A few of the thefts have been caught by home surveillance cameras set up to catch or deter vandals. A television station showed a video of a woman taking a package from a doorstep in Pasadena, Calif. The homeowner said she never got the Paula Deen electric salt-and-pepper shaker her sister had mailed her.

While it may seem extreme to install cameras to keep an eye on packages, this type of home surveillance has become more common in recent years, said Marc Horowitz, a spokesman for Brickhouse Security. The company’s sales for home security cameras have more than doubled in the past year, he said, as the cameras have become less expensive. A simple motion-activated porch camera costs about $100.

Some camera customers fear the culprit is closer to home, breaking that commandment of the cul-de-sac, Do Not Covet Thy Neighbor’s Flat-Screen TV.

Horowitz said he had heard reports from his sales representatives that some customers were buying cameras because they suspected neighbors of pilfering packages (or newspapers and plants).

UPS started a program last year called UPS My Choice,which allows a customer to receive an email or text message before a package arrives and reroute it if no one is going to be home .

UPS drivers are also trained to leave packages out of sight, said Natalie Godwin, a company spokeswoman. Godwin was with a driver in Atlanta on Tuesday when he decided not to leave a package on someone’s stoop because it was clearly an expensive computer monitor. He dropped it off nearby at the apartment complex’s office.

Drivers leave notes telling the tenants where to find packages, Godwin said.

Often, she added, "They’ll use their own judgment."

© 2012 The New York Times Company