We reported back in May that the Justice Department had commenced a criminal investigation into Uber's use of a software tool that helped drivers evade picking up local officials in places where the service had not been approved.

Portland, Oregon, was one of the cities we mentioned where Uber employed the so-called "Greyball" tool. The city has now released a scathing report detailing that Uber evaded picking up 16 local officials for a ride before April 2015, when the service finally won approval by Portland regulators.

The Greyball software employs a dozen data points on a new user in a given market, including whether a rider's Uber app is opened repeatedly in or around municipal offices, which credit card is linked to the account, and any publicly available information about the new user on social media. If the data suggests the new user is a regulator in a market where Uber is not permitted, the company would present that user with false information about where Uber rides are. This includes showing ghost cars or no cars in the area.

The city concluded that, when Uber started operating in the city in December 2014 without Portland's authorization, the Greyball tool blocked 17 rider accounts. Sixteen of those were government employees. In all, Greyball denied 29 ride requests by city transportation enforcement officers.

"In using Greyball, Uber has sullied its own reputation," the Portland Bureau of Transportation said.

Greyball is just one of myriad scandals confronting Uber. There are too many for a comprehensive list here, but one scandal concerns whether Uber stole trade secrets for a self-driving vehicle venture. Another centers around whether the company used software to defraud both drivers and riders out of money.

The Greyball report released this week was produced after the Portland City Council subpoenaed Uber for documents concerning its use of Greyball in the city. The city did not issue any penalties or fines against Uber.