The New York Times reports that Uber developed apps that identified and blocked government regulators using the app to find evidence of illegal behavior:

Yet using its app to identify and sidestep authorities in places where regulators said the company was breaking the law goes further in skirting ethical lines — and potentially legal ones, too. Inside Uber, some of those who knew about the VTOS program and how the Greyball tool was being used were troubled by it.

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One method involved drawing a digital perimeter, or “geofence,” around authorities’ offices on a digital map of the city that Uber monitored. The company watched which people frequently opened and closed the app — a process internally called “eyeballing” — around that location, which signified that the user might be associated with city agencies.

Other techniques included looking at the user’s credit card information and whether that card was tied directly to an institution like a police credit union.

Enforcement officials involved in large-scale sting operations to catch Uber drivers also sometimes bought dozens of cellphones to create different accounts. To circumvent that tactic, Uber employees went to that city’s local electronics stores to look up device numbers of the cheapest mobile phones on sale, which were often the ones bought by city officials, whose budgets were not sizable.

In all, there were at least a dozen or so signifiers in the VTOS program that Uber employees could use to assess whether users were new riders or very likely city officials.

If those clues were not enough to confirm a user’s identity, Uber employees would search social media profiles and other available information online. Once a user was identified as law enforcement, Uber Greyballed him or her, tagging the user with a small piece of code that read Greyball followed by a string of numbers.