Federal authorities have begun a criminal investigation into Uber’s use of Greyball, a software tool that the company used to evade local officials in places where the service had not been formally approved, which notably includes Portland, Oregon. This is according to Reuters , which cited two unnamed sources in its Thursday evening report.

The Department of Justice did not immediately respond to Ars’ request for comment.

“We’re not commenting,” Aaron McLear, an Uber spokesman, e-mailed Ars. “But I’ve attached our letter to Portland, Oregon, officials which gives as much detail as we have given about this technology.”

McLear included a recently published letter and attachment that was sent to Portland officials, noting that the company had not deployed Greyball in Portland since April 2015. The correspondence also says that Uber only used Greyball during a two-week period in December 2014.

In the April 21 documents, Uber also explained that a “Greyball tag” can be applied to change the standard view of an app.

“However, for a variety of routine and proper business reasons, including marketing, functionality, the safety of driver-partners, and similar reasons, at times Uber desires to display a different view to a user,” wrote Thomas J. Perrelli, a lawyer representing Uber in its dealings with Portland. (Perrelli served as the associate attorney general under the Obama administration from 2009 until 2012.)

Reuters noted that the company has not been charged with anything, and it is unclear what statute, if any, its employees may have violated. The news outlet also said that Uber has received a subpoena from a Northern California grand jury, targeting documents about how Greyball functioned and precisely where it was used.

Conceivably, Greyball could run afoul of the Computer Fraud and Abuse Act, among other laws.

As Ars reported previously, Greyball used a dozen data points on a new user in a specific market, like whether their 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 will present that user with false information about where Uber rides are. This includes showing ghost cars or no cars in the area.

In March 2017, Uber said that Greyball wasn’t just targeting regulators. The company also used the tool to prevent dispatching rides to competitors who might try to disrupt service, as well as avoid riders who might aim “to physically harm drivers.” Uber also affirmed that it used Greyball to shut down “opponents who collude with officials on secret ‘stings’ meant to entrap drivers.”

UPDATE 9:47pm ET: Abraham Simmons, a spokesman for the US Attorney's Office in San Francisco, e-mailed: "We have no comment on these reports."