document: Tencent confirmed that up to six former employees were under investigation in an ongoing anti-graft probe.
  China's biggest social network said an "internal investigation" brought to light bribery allegations.
  Several executives have been implicated in China's corruption crackdown.
  The government has been on a drive to reform the economy, the world's second largest, by clamping down on corruption in major institutions and businesses for the past two years.
  Tencent has not identified the former employees, but said that "the police have been notified" and they were awaiting further information.
  Alibaba confirmed to the Reuters news agency that Mr Lui was detained but the case was "related to his time at Tencent and has nothing to do with Alibaba".
  Mr Liu left Tencent for competitor Alibaba in 2013 to become the president of its digital entertainment unit.
  Tencent is behind China's popular messaging app, WeChat. It also owns China's largest music streaming service by subscribers and its online gaming business has been compared to that of Nintendo's and Sony's gaming units.
  Alibaba also has a large stake in Weibo, a social media site similar to Twitter as well as Chinese online video providers similar to YouTube.
  China's anti-corruption crackdown has targeted both government officials as well as company executives with many being taken into custody.
  Among recent high-profile cases in the past year were China's ex-security chief Zhou Yongkang and the former China head of pharmaceutical firm GlaxoSmithKline Mark Reilly.
summary: Chinese e-commerce giant Alibaba has said its senior executive Patrick Liu is in police custody over corruption allegations related to his previous job with internet company Tencent.