GOOG) has. And we know that China still has a chance to double the number of people online over the next several years. So what gives? I think there are two big reasons for the Fall swoon in Baidu's share price. First, there is Qihoo 360 ( QIHU). Qihoo is a much smaller player in search in China compared to Baidu, yet, it's starting from a small base for its growth. Baidu still has a $35 billion market capitalization as a company. Qihoo's market cap is $2.75 billion. Over the summer, Qihoo and others started to target Baidu. Qihoo CEO, Zhou Hongyi, has made it his goal to break Baidu's search monopoly. Most U.S. investors think of Qihoo as a browser company and therefore not as someone worth the same kind of multiple as Baidu. Yet they have 272 million monthly users. On their last earnings call, Zhou said: "If we can convert a sizable portion of these users to our search products, that will become . . . a very major market player in this area." Wall Street seems to believe him. In the last three months, Qihoo's shares are up 38% while Baidu's shares are down 24%. The second reason why Baidu's shares have been under attack is related to the rapid shift from PC users to mobile users. Just as with Google in the United States, the move makes an average search query far less profitable for Baidu compared to the good old desktop days. How will they deal with this shift? They're doing the best they can, just as Google is. Baidu is trying to make their mobile search product the best on the market. They've also signed agreements with partners like Apple ( AAPL) to provide the search behind Siri queries in China.