HTTP status codes don't usually aid political dissidents, nor are they particularly exciting. But the newly made 451 code, to be used when something is taken down for legal reasons, is a timely exception.
Status codes are used when requesting and transmitting data over the internet; for example, pulling up this page. There are five classes, 100s to 500s, and tens or hundreds of specific-code sub-classes between those numbers. You normally don’t encounter the codes unless something goes wrong — the infamous 404 error for a page not found, for example.
The Internet Engineering Steering Group (IESG), a group of engineers who help review and update the standards used on the internet, has approved a new status code: 451 (a reference to Ray Bradbury's novel Farenheit 451), to be used when access is denied as a consequence of legal demands. That could be something like a takedown notice served to Google, or censorship by a national government.
As explained by Mark Nottingham, chair of the IETF working group that first looked at the idea, having a specific status code for censorship could prove useful in a number of ways.
It’s a standardised, machine-readable way of saying that a page has been taken down as a result of censorship, which means that it will be easier to determine how many blog posts or videos or tweets get taken offline for non-technical reasons. It’s also a good passive-aggressive way for hosting services like YouTube and Google to point the finger of blame. [IETF via Engadget]