After Snowden: How vulnerable is the internet?

The internet was designed to be free and open. Eight months after Edward Snowden's first leaks of classified information, is that still the case?

The technology pioneers who designed the net's original protocols saw their creation as a way to share information freely across a network of networks.

Yet Edward Snowden's leaks of classified documents from the US National Security Agency have revealed that American spies - and their British counterparts at GCHQ - now use that very same internet to sweep up vast amounts of data from the digital trail we leave every day.

It isn't simply that they mine social media updates and the information we already give to companies. The NSA and GCHQ have allegedly tapped into the internet's structure.

An ever-growing network

Much like the universe in the aftermath of the Big Bang, the internet is expanding. From humble beginnings as a project within the US Department of Defense, the net has grown with each technological advance.

This growth has required an ever-expanding physical infrastructure of routers, cables, data centres and other hardware. Between 1994 and 2013 they multiplied many times over.

Internet backbone

The giants of the net are companies and organisations that provide the so-called internet backbone, transferring data around the net over high capacity fibre optic cables.

This map, made using data from Peer 1's Map of the Internet, shows the relative connectedness of organisations online. The biggest blobs - those with the most connections - are the backbone firms, dwarfing the likes of Google and Amazon.

How data is transferred

Almost everything we do online passes through a backbone company. If, for example, a student living in London sends an email to a friend in Brazil, the message will hop around the network and will often travel through a backbone firm like Level 3 Communications in the USA, which describes itself as "network provider for much of the world's communications infrastructure".

So if the cables of firms like Level 3 were intercepted, the security agencies would have access to a huge amount of the world's internet traffic.

In November 2013, the New York Times reported that the NSA may have accessed Google and Yahoo via Level 3's cables.

In statement, the firm told the BBC: "We comply with applicable laws in each of the countries where we operate. In many instances, laws forbid us from revealing any details relating to our compliance, and make it a crime for us to discuss any required access to data.

"Some media sources have incorrectly speculated that we have agreements with governments where we voluntarily provide access to network data even when we are not compelled to do so. That is incorrect. Customer privacy is paramount to our business. We do not allow unauthorised access to our network by any entity and will continue to operate our network to protect and secure our customers' data, while adhering to the laws that apply to Level 3 as well as all other telecommunications providers."

Tapping cables

Land-based cables are not the only physical access points for intercepting data.

Snowden documents published in the Guardian last June indicate that the US and Britain's spy programmes aimed at "mastering the internet" include tapping the undersea cables through which data - and phone calls - flow.

The documents claim GCHQ was able to monitor up to 600 million communications every day. The information describing internet and phone use was allegedly stored for up to 30 days in order for it to be sifted and analysed.

GCHQ declined to comment on the claims but said its compliance with the law was "scrupulous".

The future

The scale of the NSA's data collection is hard to comprehend. And opinions about its legitimacy are divided: some believe it is a vital bulwark against terror attacks while others insist the programmes are dangerous infringements of civil liberties.

The Snowden revelations may lead to a change in how governments and large organisations use the internet.

There has been talk of the internet "breaking up" so that, for example, communications which start and end in Europe only travel along European cables.

"Data is power, and data is money," security expert Bruce Schneier, who has analysed the Snowden documents for journalist Glenn Greenwald, told the BBC.

"These discussions about who has control of data are bigger than the NSA, bigger than surveillance, and they are the key questions of the information age."

But technology experts say this would make business more difficult to carry out online and may make the easy global access to which we have become accustomed a thing of the past.

"I don't think we know what the internet is going to transform into because of this," Mr Schneier said.