An abbreviation of the full name Microsoft resembling the rather bogus way Windows 9x's VFAT filesystem truncates long file names to fit in the MS-DOS 8+3 scheme (the real filename is stored elsewhere). If other files start with the same prefix, they'll be called micros~2 and so on, causing lots of problems with backups and other routine system-administration problems. During the US Antitrust trial against Microsoft the names Micros~1 and Micros~2 were suggested for the two companies that would exist after a break-up.