Qihoo 360 gave away the thing everyone else sold. In China, antivirus software was a paid product until Zhou Hongyi made his free. Hundreds of millions of people installed it, and Qihoo turned that reach into a web browser, a search box and an ad business. When it listed in New York in March 2011, China's internet was the hottest trade on Wall Street. Qihoo's shares more than doubled on the first day.

Give Away the Shield

Zhou Hongyi and Qi Xiangdong founded Qihoo in Beijing in 2005. Zhou had sold an earlier startup to Yahoo. Qihoo's bet was that security software could be free if the company owned the user's desktop. Its 360 Safe Guard cleaned up malware, and its free antivirus followed. Then came the 360 browser and a homepage of links that millions saw every day. Advertising and online games paid the bills.

Wall Street, Then Shanghai

Qihoo priced 12.1 million American depositary shares at $14.50 on March 29, 2011, above its $10.50 to $12.50 range. They began trading on the New York Stock Exchange as QIHU the next day and closed up 134 percent. Five years later, a group led by Zhou took the company private in a deal worth about $9.3 billion. In 2018 it relisted on the Shanghai Stock Exchange as 360 Security Technology.

Cover: The Guardian Angel, Jacopo de' Barbari. Art Institute of Chicago, public domain. Chosen for a guardian angel (free protection).