Qihoo 360

Second-largest search engine in China; major challenger to Baidu in search advertising with a large security and browser user base providing audience scale

Qihoo 360 Technology Co. Ltd. is a major Chinese internet and cybersecurity company founded in 2005, best known for its free antivirus and security software that rapidly gained dominance in the Chinese PC security market. Beyond security, Qihoo 360 expanded aggressively into search with the launch of 360 Search (So.com, formerly haosou.com), which at its peak captured roughly 20-30% of China's search market, making it the second-largest search engine in China behind Baidu. The company also operates a browser, mobile security apps, and a suite of internet services reaching hundreds of millions of users across China. In the AdTech ecosystem, Qihoo 360's primary monetization vehicle is 360 Dianjing (360点睛), its search advertising and digital marketing platform. This platform allows advertisers to bid on keywords and display ads across 360 Search and its network of affiliated properties, competing directly with Baidu's Phoenix Nest advertising system. The company's massive installed base of security software and browser users provides a significant first-party data advantage for targeting and audience segmentation. Qihoo 360 was originally listed on the New York Stock Exchange but was taken private in 2016 through a leveraged buyout led by a Chinese investor consortium, and subsequently relisted on the Shanghai Stock Exchange's STAR Market in 2018 under the ticker 601360. The company remains a significant player in Chinese digital advertising, leveraging its security and browser ecosystem to deliver search and display advertising solutions to Chinese businesses of all sizes.