Slashdot reader joshuark summarizes this walk down memory lane from the tech site MakeUseOf:
Facing real competition from Digital Research's DR DOS, Microsoft secretly embedded a sabotaging mechanism known as "AARD code" into beta versions of Windows 3.1 to prevent it from running on Digital Research's competing DR DOS operating system.This code triggered fake, alarming error messages to convince developers that DR DOS was unstable... Although Microsoft disabled the feature in the final retail release, the California-based firm Caldera, Inc., which had acquired DR DOS assets, sued Microsoft for anti-competitive practices.Microsoft settled the lawsuit out of court in 2000 for $280 million, a ...