As long as you use the software that is claimed to kill virus on your computer, somehow it will cause you to click a button to set your homepage to be QIHU's search engine. And many people (usually peasants or older people) don't know how to remove that stupid setting. So some people end up using QIHU's search engine. But those kind of people are usually computer illiterate and don't search that much.
QIHU's behavior is really despicable.