What's behind Qihoo 360's squabbles with rivals in the past year?

Q: What' behind Qihoo 360' squabbles with rivals in the past year?

A: Qihoo 360 Technology Co.'s highly-anticipated IPO on the New York Stock Exchange in March totaled US$ 176 million. Shares in the leading anti-virus software company more than doubled to US$ 34 soon after the public debut. But beyond the market buzz, Qihoo has also come under a harsh light after major competitors accused the company of unethical business practices last fall.

Qihoo vs. Tencent: What started out as a series of lawsuits escalated into a public mudslinging contest when Qihoo and China's largest internet company, Tencent Holdings Ltd., began accusing each other of spying, hacking and leaking users' private information, as well as deliberately releasing malware. Tencent operates the popular instant-messaging platform QQ, which has over a billion users.

Tencent announced in November 2010 that because Qihoo's antivirus software was destroying QQ's ability to protect user information, the company was shutting down QQ on any computers with Qihoo software installed, forcing users to choose between the two companies. According to Tencent, about 15 million users removed Qihoo software as a result.

The spat prompted a legal investigation by the Chinese Ministry of Industry and Information Technology and the Ministry of Public Security, which in late November publicly rebuked the two companies and forced them to settle any remaining issues.

Qihoo vs. Kingsoft: With the QQ-Qihoo rivalry putting a dent in Qihoo's popularity, other anti-virus software companies have begun to seek a stronger market position. In December 2010, anti-virus software rival Kingsoft accused Qihoo 360 of collecting and leaking users' private information; Qihoo responded with a countersuit.

Kingsoft also has another lawsuit pending against Qihoo, alleging that Qihoo software is blocking the installation of Kingsoft programs under the guise of "software incompatibility."

Qihoo vs. Baidu: Also in December 2010, China's top search engine company Baidu won an unfair competition suit against Qihoo, after proving that Qihoo's software had classified some of Baidu's products as malware, and that Qihoo had encouraged users to uninstall Baidu applications.