In 2004 Yahoo! gave up email records to the Chinese government which were then used to jail a dissident. According to Yahoo! General Counsel Michael Callahan at a U.S. Congressional hearing on February 15, 2006, Yahoo! didn’t know this was a political rather than ordinary criminal matter.
However, now there is evidence that at all relevant times Yahoo! knew or should have known that this was a political case. The case is discussed in deatil by Rebecca MacKinnon, Assistant Professor at the University of Hong Kong at RConversation: Shi Tao’s case: Yahoo! knew more than they claimed.