Many companies have found the internet to be a disruptive technology - one that destroys old business models by providing products more cheaply and efficiently. Now Microsoft, which makes the software that powers personal computers and much of the internet, is itself threatened by disruptive technologies. It is a salutary reminder that even the most profitable business model is not immune to competitive forces - and that should be cause for rejoicing in a market economy.

Only a few years ago, Microsoft seemed to have an unbreakable stranglehold on the information technology world. It had used the dominant position of the Windows operating system to grab market share for the Office suite of products, to all but destroy Netscape with its Internet Explorer browser and to marginalise rivals of Windows Media Player. Its model of building interlocking applications that provided a comprehensive, integrated experience for users seemed invincible.