Here's what Volkswagen did and how they got caught

The company cheated US diesel emissions tests for seven years.

It did so through a clever piece of software that could identify when it was being tested and reduce harmful exhaust so it looked like the cars met requirements, when in fact they didn't.

Volkswagen was caught out by independent testing carried out by a clean-air advocacy group, called the International Council on Clean Transportation, which tested the cars themselves because they thought they were such a great example of how diesel can be a clean fuel.

Here's a rundown on what happened and when.