A
arachnid
And what they are not supposed to do is to force the market to bear the
insanely high prices they charge and keep jacking up the price by having a
virtual monopoly.
Microsoft's monopoly isn't virtual. Courts all over the world, including
US and European, courts, have ruled Microsoft to be a defacto monopoly
under their laws. The legal definition of a monopoly only requires that a
company have sufficient market share that it's free of competitive
pressures in setting prices, features, terms of use, etc. Typically that
happens when a company owns around 90% of the market.
Just for fun, here's an interesting page that does a market simulation for
various types of companies and market situations:
http://www.egwald.com/economics/econpage.php3
It's educational to leave all other conditions equal while stepping
down through the number of competitors until you arrive at a monopoly. To
simplify comparisons it's best to use a different browser tab for each
computation so you can flip back and forth.