Big tech companies love their lawyers and hate anything that could be regarded as competition. They're also known for rather dodgy practices. MS-DOS 1 was a slightly tweaked and ported version of QDOS, which in itself was a slightly tweaked version of CP/M. Back in the days of Windows 95, there was a popular email / newsgroup signature tag-line:

Windows 95: 32-bit extensions to a 16-bit GUI for an 8-bit operating system based on 4-bit code, written by a 2-bit company that can't stand 1 bit of competition.

Nowadays it's Apple that generates the headlines with its lawyers. It saw that Samsung's Galaxy Tab was getting a bit too popular for its liking so their lawyers managed to convince a judge to remove the Samsung product from the European market, despite the fact the supposed imitative factors would also apply to most iPad rivals (oh, and they faked some of their evidence - the Samsung product has a different aspect ratio and screen resolution to the iPad yet they were shown as the same size in the court submissions. Hmm...)