The U.S. Department of Justice has opened up a criminal investigation into Uber’s use of a tool that allowed it to track users and evade regulators.

The software tool, dubbed Greyball, allowed the ride-hailing service to track select users and show them a different version of the app. Additionally, Greyball obscured the real location of Uber cars, allowing it to slip through government officials clamping down on the service in certain U.S. cities including Portland.

Alongside these features, Greyball gathered credit card information and location data of users and was able to determine if a user had a credit card account affiliated with a credit union used by police. It also checked a user’s social media profiles to determine if they were in law enforcement.

According to Portland transportation officials, Uber used Greyball to evade 16 Portland Bureau of Transportation officials and denied them rides before the ride-hailing service was authorized to be used in the city.

Reuters says that the criminal investigation into the use of Greyball is still in its early stages and it’s not yet known if anyone will be charged.

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