The result of Microsoft's rapid turn around in Internet policy from "The MSN is the way to go" to "We are fully committed to the Internet". Billions of dollars went into software research into this world wide web browser which was given away for free in order to take market/mind share from Netscape's Navigator.
Also the subject of numerous anti-competitive suits against Microsoft, as Microsoft used its monopoly power to require that Internet Explorer be installed with Windows.
With the recent (April, 2000) legal findings against Microsoft that it indeed was a monopoly and did abuse its monopoly, the decision to create and give away IE might yet come back to haunt the software behemoth.