Qihoo 360 yesterday squared off with Tencent in a mainland court, in a landmark case involving the Chinese internet industry's first anti-monopoly litigation. The Guangdong People's High Court heard Qihoo, which sells antivirus software, accuse Tencent of abusing its dominant market position in a dispute between the two companies in 2010. Qihoo is seeking 150 million yuan (HK$184.2 million) in damages from Tencent. The judge said the court hearing first had to define the instant messaging market, and whether it was dominated by Tencent - and whether it had abused its position. Tencent denied dominating the instant messaging market, saying its QQ system was only one of a range of similar services available. Tencent's lawyer said the instant messaging market was completely open, adding that QQ did not have pricing power, saying that 87 per cent of its users would turn to other tools if it tried to charge for its service, which is now free. David Stallibrass, a former director of the Office of Fair Trading in London, was an expert witness for Qihoo, and Jiang Qiping, secretary general from an IT arm of the Chinese Academy of Social Sciences, defended for Tencent. Stallibrass said Tencent's high market share made it difficult for others to enter the market. Zhao Ye, Qihoo's lawyer, separately said the QQ IM system operated by Tencent had topped 70 per cent in the past five years, and it had abused its position. He said Tencent had restricted QQ users from using Qihoo software and monopolised the market through tie-in sales of software and distributing QB, a virtual currency for purchasing services. He said this strangled competition. Tencent's revenue was 28.4 billion yuan last year. The companies' dispute dates back to 2010, when Qihoo alleged that Tencent let its QQ software scan users' computers for personal data, prompting Qihoo to issue tools to protect QQ users' privacy. Tencent denied the allegation, and responded by not allowing its users to use ITS QQ's software if they used Qihoo 360 software. In 2010, the No 2 Beijing Intermediate People's Court ruled that Qihoo had defamed Tencent, and ordered Qihoo to pay 400,000 yuan.