For a while, the wireless Internet connection Christine and Randy Brodeur installed last year seemed perfect. They were able to sit in their sunny Los Angeles backyard working on their laptop computers. But they soon began noticing that their high-speed Internet access had become as slow as rush-hour traffic on the 405 freeway.

"I didn't know whether to blame it on the Santa Ana winds or what," recalled Mrs. Brodeur, the chief executive of Socket Media, a marketing and public relations agency. The "what" turned out to be neighbors who had tapped into their system. The additional online traffic nearly choked out the Brodeurs, who pay a $40 monthly fee for their Internet service, slowing their access until it was practically unusable.