The more things change, the more they stay the same.
You may not know that commissions are paid by some online stores to web sites that provide links to the stores. Small businesses use affiliate links for some extra income; charities use them for fundraisers. When you click on the link to Amazon from my Web Favorites page to do your shopping, I get a trivial amount of money from Amazon. (Thank you! Buy your Dell computers that way too, okay?)
When you install the new version of Kazaa (or several other programs), you may be asked if you want to participate in an “online affiliate” program, described in gentle terms as a painless way to help the software developer make some money. When you agree, software will be stealthily installed on your computer that diverts all of your shopping commissions to Kazaa, even if you enter a store through another site that has its own affiliate agreement. And the software diverting the commissions isn’t removed if you uninstall Kazaa. Here’s an article about the “stealware.” (New York Times – free registration required.)
It’s not a reason not to use Kazaa – just be careful what you click on when you install offbeat programs!