This summer, lawyers at United Airlines noticed that someone had built an almost perfect replica of the company’s website.

This digital clone offered all the same buttons and menus for booking flights, hotels and rental cars. It included the same blue links for tracking frequent flier miles and browsing discount deals. It even used the United brand name and logo.

So United’s lawyers sent a formal takedown notice accusing the site of violating its copyrights.

Div Garg, whose tiny company built the replica site, promptly changed the site’s name to “Fly Unified” and removed the United logo. He was not interested in stepping on United’s copyrights. He and his company built their United.com replica as a training ground for artificial intelligence.

Mr. Garg’s company, AGI, is among a number of Silicon Valley start-ups that have spent the past several months recreating popular websites so that A.I. systems can learn to navigate the internet and complete specific tasks on their own, like booking flights. If an A.I. system learns to use a replica of United.com, it can use the real site, too.

These new shadow sites are a significant part of the tech industry’s efforts to transform today’s chatbots into A.I. agents, which are systems designed to book travel, schedule meetings, build bar charts and complete other computing tasks. In the coming years, many companies believe, A.I. agents will become increasingly sophisticated and could replace some white-collar workers.

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