"Wi-Fi is in the air, and it is a very low curb, if you will, to step up and use it," said Mike Wolf of ABI Research, a high-technology market research company in Oyster Bay, N.Y.

This is especially true, Mr. Wolf said, because so many users do not bother to secure their networks with passwords or encryption programs. The programs are usually shipped with customers' wireless routers, devices that plug into an Internet connection and make access to it wireless. Many home network owners admit that they are oblivious to piggybackers.

Some, like Marla Edwards, who think they have locked intruders out of their networks, learn otherwise. Ms. Edwards, a junior at Baruch College in New York, said her husband recently discovered that their home network was not secure after a visiting friend with a laptop easily hopped on.

"There's no gauge, no measuring device that says 48 people are using your access," Ms. Edwards said.

When Mr. Wolf turns on his computer in his suburban Seattle home, he regularly sees on his screen a list of two or three wireless networks that do not belong to him but are nonetheless available for use. Mr. Wolf uses his own wired network at home, but he says he has piggybacked onto someone else's wireless network when traveling.

"On a family vacation this summer we needed to get access," Mr. Wolf recalled, explaining that his father, who took along his laptop, needed to send an e-mail message to his boss on the East Coast from Ocean Shores, Wash.. "I said, 'O.K., let's drive around the beach with the window open.' We found a signal, and the owner of the network was none the wiser," Mr. Wolf said. "It took about five minutes."

Jonathan Bettino, a senior product marketing manager for the Belkin Corporation, a major maker of wireless network routers based in Compton, Calif., said home-based wireless networks were becoming a way of life. Unless locking out unauthorized users becomes commonplace, piggybacking is likely to increase, too.