Twitter has announced that it now has the technology to selectively block tweets on a country by country basis.

Twitter has said on its blog it now has the right to censor specific tweets in some countries. Twitter has explained in its blog post

As we continue to grow internationally, we will enter countries that have different ideas about the contours of freedom of expression. Some differ so much from our ideas that we will not be able to exist there. Others are similar but, for historical or cultural reasons, restrict certain types of content, such as France or Germany, which ban pro-Nazi content.

They also state that until now they have only been able to remove content globally and they will only withhold content from a specific country while keeping it available to the rest of the world.

Twitter state that they will transparent  in the filtering process and it will only be done in response to a specific valid legal request. Any content they withhold in response to such a request will clearly be identified to users in that country.

As part of that transparency they share any action at http://chillingeffects.org/twitter which makes it easy to find take down notices related to Twitter.

In a follow up on the twitter blog they answer a few questions and give example on how a tweet may appear to users.

Soon after the Twitter announcement users were trying to find a way around any blocks and found there may be an easy way around it by changing a country setting as shown in this post.