Governments will not always be able to disguise which content they restrict across the Web thanks to a new error code which will warn users of content restricted through censorship.

On Friday, the group responsible for Internet standards, the Internet Engineering Steering Group (IESG), approved a new HTTP code to differentiate between Web pages which cannot be shown for technical reasons and others which are unavailable for non-technical reasons, such as governmental censorship.

Status codes, available within the 100s to 500s, are most commonly encountered when something goes wrong -- such as a server downtime, for example, which prevents a user from accessing a Web page. The common 404 error tells users a page has not been found, but now 451 is coming into its own as a way to track other restrictions.

Online censorship is on the rise. Governments in the European bloc force ISPs to restrict access to websites linking to pirated content, China has its ever-famous "Great Firewall" which heavily restricts the Web, and countries including Russia and South Korea are also cracking down on access.

It isn't always easy to work out whether a Web page is down because of technical reasons or governmental meddling. However, a new Internet protocol could change that.

Mark Nottingham, chair the IETF HTTP Working Group -- developers of the Internet's core HTTP protocol -- explained in a blog post while the 403 error status code says "Forbidden," it does not specify if there are legal reasons for restricting content.

However, status code 451 -- a hat tip to Fahrenheit 451 -- can now be used to distinguish pages unavailable due to censorship.

"As censorship became more visible and prevalent on the Web, we started to hear from sites that they'd like to be able to make this distinction," Nottingham said.

In addition, some organizations said they would like to be able to spider the Web for pages containing a censorship-based error code in order to catalog examples of censorship.

While a HTTP header could have been added to 403 pages instead, standardized, machine-readable 451 codes have already begun to gain traction after use on experimental websites.

Nottingham predicts that 451 will likely be used more on Web servers than by network-based intermediaries, as websites including Twitter, Facebook, Google and Github are forced to censor content in certain countries and jurisdictions.

See also: China's 'Great Cannon': Taking censorship across country borders

There are also discussions underway concerning how 451 could be leveraged to prompt users to access restricted content in other ways.

Nottingham commented:

"In some jurisdictions, I suspect that censorious governments will disallow the use of 451, to hide what they're doing. We can't stop that (of course), but if your government does that, it sends a strong message to you as a citizen about what their intent is. That's worth knowing about, I think."

Either way, 451 is a start in giving the general public a better idea of what their government's practices are when it comes to censorship.

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