I found the following in a slashdot.org posting. I'm not claiming it is true but it seems to have quoted some documentation in public archives. I'm reposting it in order to keep it documented for future purposes.

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In 1991, Microsoft employees launched an exceptionally dastardly plan to kill another competitor, DR DOS. DR DOS sales threatened MS-DOS, the early predecessor to Windows 95 that established Microsoft's operating system monopoly. DR DOS sales were on the rise--they doubled from $15 million in 1990 to $30 million in 1991. They soared again to $15 million in the first quarter of 1992 alone. Then disaster struck.

Microsoft was writing Windows 3.1, an important upgrade to the hugely popular Windows 3.0. In September 1991, a plan was hatched to use this upgrade to kill DR DOS. In an email discovered by the Dept. of Justice, the head of Windows development and Microsoft VP David Cole wrote, "aaronr had some pretty wild ideas after three or so beers--earleh has some too." The plan was to plant code into Windows which would "put competitors on a treadmill" and cause the system to "surely crash at some point shortly later." In order words, Windows would intentionally bomb if it detected DR DOS.

At this time, many computer vendors were considering switching from MS-DOS to the superior, cheaper DR DOS. Microsoft was especially concerned about IBM. Wooing these PC vendors was crucial to the future success of DR DOS, as was the good will of "early-adopters" (i.e., technically savvy users who drive new trends in the computer industry).

These vendors and early-adopters were also the same people who received a Christmas "beta" pre-release of Windows 3.1. They discovered--to their horror--that using DR DOS would cause vague system errors to pop up in Windows 3.1; they dumped DR DOS in droves. By the fourth quarter of 1992, sales of DR DOS had dropped from $15 million to only $1.4 million. The once mighty competitor became a has-been and was sold to Novell and later Caldera.