Here is how the Volkswagen scheme worked, according to the federal Environmental Protection Agency: The cars’ software turned on the pollution-control equipment only during inspections. No human intervention needed. The software could silently deduce that an inspection was taking place based on the position of the steering wheel (cars hooked up to emissions meters don’t make turns), the speed of the vehicle, how long the engine had been running and barometric pressure. The driver and the inspector were none the wiser.

When the test was done and the car was on the road, the pollution controls shut off automatically, apparently giving the car more pep, better fuel mileage or both, but letting it spew up to 35 times the legal limit of nitrogen oxide.

This cheating was not discovered by the E.P.A., which sets emissions standards but tests only 10 to 15 percent of new cars annually, relying instead on “self certification” by auto manufacturers. The scam came to light when engineers at West Virginia University road-tested Volkswagen cars that had passed emission inspections. The cars, the engineers discovered, actually pumped out more pollutants when they were in the real world. Far from trying to make trouble for Volkswagen, the engineers had been hired by the International Council on Clean Transportation, a clean-air advocacy group that hoped to use Volkswagens to show European regulators how efficiently diesel cars could meet the strict emissions limits set by the United States.

After months of denials, Volkswagen admitted it had programmed cheating into the software.

Mr. Moglen, a lawyer, technologist and historian who founded the Software Freedom Law Center, has argued for decades that software ought to be transparent. That would best serve the public interest, he said in his 2010 speech.

“Software is in everything,” he said, citing airplanes, medical devices and cars, much of it proprietary and thus invisible. “We shouldn’t use it for purposes that could conceivably cause harm, like running personal computers, let alone should we use it for things like anti-lock brakes or throttle control in automobiles.”