The assault on software giant Microsoft
Linux and friends
Microsoft may have a monopoly right now, says Mr Colony, but "protection of a monopoly is tricky". And there are plenty of challengers ready to put Microsoft's durability to the test.
Foremost among them is the Linux operating system.
Rivalling Windows, this "open source" software project is developed by an online community of volunteers, but backed by big and small corporate players (like IBM and Red Hat) who provide support and tailor the software for individual business needs.
Linux, its champions say, is more stable and secure than anything Microsoft has ever produced.
It is cheap - even free if you are computer-savvy enough to install and maintain it - and much more customisable, because the code that makes it tick is neither a secret nor copyrighted by a single firm.
These days Linux is not just the software of choice for geeks; recently even the stolid bureaucrats of Bavaria's capital Munich decided to switch all their computers to Linux.
China, South Korea and Japan, meanwhile, have joined forces to develop an Asian flavour of Linux, to ensure they are not in thrall to Microsoft.
Other parts of the empire are under attack too, such as the hugely profitable "Office" suite.
Don't want to pay for a word processor, spreadsheet, database and presentation tool? Download OpenOffice. It won't look as nice as Office 2003, but it's free and fully featured.
Editing pictures? You don't have to pay for Microsoft's "image suite". The open source "Gimp" is powerful, while Google's free Picasa will meet the everyday needs of most consumers.
The browser war
Microsoft's biggest worry, though, should be the huge success of Mozilla Firefox, the open source web browser.
Apple takes a bite
"Microsoft is not an innovator or transformer right now," says Forrester's George Colony. Many rivals are more focused and nimble.
"Companies are not afraid of competing with Microsoft anymore," says Marc Benioff, the boss of salesforce.com, which offers a service over the internet which competes with Microsoft in the lucrative market for "customer relationship management" software.
Forrester boss George Colony predicts that there will "a crisis at Microsoft, where they decide their model is broken".