Bots are not kicked off the system, but rather “speedbumped” — slowed down, sent to the end of the line or given some other means of interference, to allow a regular customer through.

“We’re not trying to stop anybody from buying tickets,” Mr. Carnahan said. “We’re just trying to make sure that a fan can buy the tickets.”

Ticketing bots are often inexpensive and programmed in countries beyond easy reach of American law enforcement. Rob Rachwald of the computer security company FireEye, which is not working with Ticketmaster, points out that one site — available in English and Russian — charges just $13.90 for the keys to 10,000 Captchas, those squiggly lines that test whether a potential customer is human.

In January, Ticketmaster replaced most of its old Captchas with newer and more sophisticated versions. The company is also introducing a system for mobile devices that aims to eliminate Captcha-style tests altogether.

Live Nation will not say how many of the 148 million tickets it sells each year are bought using bots, and in many cases it may not know. Few ever admit to using the programs; official groups like the National Association of Ticket Brokers, which represents many of the biggest resellers, condemn them and say they support anti-bot measures. But people at nearly every level of the concert business blame bots for wreaking all kinds of economic havoc.

“There are sold-out shows in reserved-seat houses in New York City where we will have 20 percent no-show, and that 20 percent will be down in the front of the house,” said Jim Glancy of The Bowery Presents, an independent concert promoter in New York. “It’s speculators who bought a bunch of seats and didn’t get the price they wanted.”