One day after professor Chen Hongguo posted his resignation letter on Weibo that has triggered hot discussion on academic freedom in China on December 23, 2013, his letter was deleted. A search on professor Chen's name on Sina Weibo shows the following message: 

根据相关法律法规和政策,“谌洪果”搜索结果未予显示。

According to relevant regulations and policies, search results for “Chen Hongguo” are not displayed.