下載自路透 A man holds an iPhone as he visits Sina&#039;s Weibo microblogging site in Shanghai May 29, 2012. China&#039;s Sina Corp has introduced a code of conduct for users of the local version of Twitter amid accusations of censorship to rein in what has grown into a raucous online forum to air political and social grievances. The code of conduct, first announced earlier this month, stipulates that users of Sina&#039;s Weibo microblogging site cannot post information that is against the principles of the constitution, cannot harm national unity, disclose state secrets or publish false information, among other rules. REUTERS/Carlos Barria  (CHINA - Tags: MEDIA) - RTR32S2O