China imposed tighter control on purchasing Olympic Games tickets, especially for the opening and closing ceremonies. An official document of Beijing’s local authorities gave orders to effectively monitor "enemies" during the Olympics. The list includes international terrorists, ethnic or sectarian separatists, opponents with hostile attitude, hardliner Falun Gong practitioners, criminal offenders, people who are seriously dissatisfied with the society and petitioners who came to Beijing to appeal their cases.
Source: Voice of America, February 20, 2008
http://www.voanews.com/chinese/w2008-02-20-voa35.cfm