From the Twitter company blog:
Starting today, we give ourselves the ability to reactively withhold content from users in a specific country — while keeping it available in the rest of the world. We have also built in a way to communicate transparently to users when content is withheld, and why.
We haven’t yet used this ability, but if and when we are required to withhold a Tweet in a specific country, we will attempt to let the user know, and we will clearly mark when the content has been withheld.
“Relax: Twitter’s New Censorship Policy Is Actually Good for Activists” ^ really good info. go take a gander at that...