Yahoo Inc. helped the United States government spy on citizens by allowing it to search through millions of user emails for certain key phrases, according to a new report by Reuters journalist Joseph Menn.

Citing “people familiar with the matter,” Menn said that last year Yahoo developed a software tool capable of sifting through its customers’ incoming emails to search for information provided by U.S. agencies such as the National Security Agency and the Federal Bureau of Investigation.

According to Menn, this is the first known case of an American company agreeing to spy on all incoming messages in real time rather than simply scanning already stored emails for a select number of users.

“It is not known what information intelligence officials were looking for, only that they wanted Yahoo to search for a set of characters,” Menn wrote. “That could mean a phrase in an email or an attachment, said the sources, who did not want to be identified.”

In his report, Menn notes that if Yahoo received this sort of request from the U.S. government, it is likely that other major Internet companies were also approached, but it is not known which, if any, complied with the requests as Yahoo allegedly did.

“Yahoo is a law abiding company”

According to the report in Reuters, the decision to comply with the request for access to Yahoo’s emails fell to company Chief Executive Marissa Mayer, and it may have been the reason for the departure of Yahoo Chief Information Security Officer Alex Stamos, who since moved on to Facebook Inc.

Yahoo did not confirm or deny the accusations in Reuters’ report, but a spokesperson released a brief statement, saying: “Yahoo is a law abiding company, and complies with the laws of the United States.” According to Reuters, Yahoo has declined to make any further comments on the matter.

In 2013, NSA documents leaked by Edward Snowden revealed that the agency gathers data transmitted between servers from several major internet companies, including Yahoo. At the time, a Yahoo spokesperson said that the company has “strict controls in place to protect the security of our data centers, and we have not given access to our data centers to the NSA or to any other government agency.”

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