An Internet security giant sued China's largest search engine enterprise in a Beijing court on Friday, claiming unfair competition.

Qihoo 360, a company offering Internet security services, claims that Baidu Inc, the most popular search engine in the country, is unfairly promoting its anti-virus software online.

When a computer user looks for Qihoo 360's anti-virus program on Baidu, the search engine will introduce and promote its own software, according to a legal representative of Qihoo 360.