Google is a great search engine. This greatness is not just due to its ability to find things, an important component of any search engine, but its company's benevolent philosophy was also an important part of Google's rise.
In contrast, we have Yahoo!, a company which makes a search engine so exciting, they needed to put an exclamation mark after it. From Slashdot comes this Yahoo! News article syndicated (or perhaps derived?) from eWeek (confusing, but still humorous), explaning how Yahoo's spyware-blocking toolbar does not automatically detect certain programs considered adware, including Claria (née Gator) and WhenU. Having had to remove these programs from the computers of various friends, family, and associates, I can assure you that they are "evil." Concidentally, Yahoo has a partnership with Claria.
The enlightened web surfer would obviously never install a browser toolbar made by a company which was in bed with adware. Alas, some web users still use Yahoo! as their primary search engine, not realizing there is (or, even more strangely, actively eschewing) a better alternative. Yet, suppose their computer is infected with adware. Not realizing the semantic differences between spyware and adware, or perhaps just missing the option to enable adware scanning, they run Yahoo!'s program. When the problem stays unresolved, some of them will give up, living with the constant advertisements.
But other users will attempt to find new programs. Hopefully, their fate in Yahoo! will be shaken enough that they will step into the light, so to speak.