Yahoo developed software to help U.S. intelligence search its customers’ incoming emails, Reuters reported Tuesday.

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The internet portal allegedly developed a program to scan incoming email and attachments for key phrases to comply with a classified directive sent to Yahoo’s legal team.

The report indicates that the software was developed without consultation with Yahoo’s security team, including prominent then-Chief Information Security Officer Alex Stamos.

Reuters says Stamos left the company after his team discovered the surveillance software, which they initially believed to be hackers attacking the system.

The report also says that employees were disappointed that chief executive Marissa Mayer decided to accept the 2015 directive and not challenge the order in court.

In 2007, five years before Mayer became CEO, Yahoo had challenged and lost a court fight over a directive forcing it to search customer accounts without a warrant.

Experts told Reuters this is the first case of a company agreeing to surveil all of its incoming emails. Large web-based companies have traditionally held an antagonistic relationship with intelligence agencies and refused to provide software to aid in surveillance.

Yahoo recently announced plans to have Verizon buy the company in a $4.8 billion deal. Yahoo has returned to the headlines in recent weeks after discovering a data breach compromising half a billion user accounts.