that is already struggling with an array of recent business and legal issues.

Uber lawyers said in letters to Portland authorities, which Portland made public in a report last week, that the Greyball technology was used "exceedingly sparingly" in that city, before the service was approved there in 2015.

The nature of any potential federal criminal violation, and the likelihood of anyone being charged, is unclear. The investigation is still in its early stages, the sources said.

The technology at issue in the criminal probe helped Uber tag some users so that they saw a different version of its standard app, Uber said in a blog post in March.

Uber said Greyball obscured the real location of Uber cars in various circumstances, including the possibility of physical threats or merely to testbirths
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