NSA Prism program taps in to user data of Apple, Google and others

• Top-secret Prism program claims direct access to servers of firms including Google, Apple and Facebook • Companies deny any knowledge of program in operation since 2007 • Obama orders US to draw up overseas target list for cyber-attacks

The National Security Agency has obtained direct access to the systems of Google, Facebook, Apple and other US internet giants, according to a top secret document obtained by the Guardian.

The NSA access is part of a previously undisclosed program called Prism, which allows officials to collect material including search history, the content of emails, file transfers and live chats, the document says.

The Guardian has verified the authenticity of the document, a 41-slide PowerPoint presentation – classified as top secret with no distribution to foreign allies – which was apparently used to train intelligence operatives on the capabilities of the program. The document claims "collection directly from the servers" of major US service providers.

Although the presentation claims the program is run with the assistance of the companies, all those who responded to a Guardian request for comment on Thursday denied knowledge of any such program.

In a statement, Google said: "Google cares deeply about the security of our users' data. We disclose user data to government in accordance with the law, and we review all such requests carefully. From time to time, people allege that we have created a government 'back door' into our systems, but Google does not have a back door for the government to access private user data."

Several senior tech executives insisted that they had no knowledge of Prism or of any similar scheme. They said they would never have been involved in such a program. "If they are doing this, they are doing it without our knowledge," one said.

An Apple spokesman said it had "never heard" of Prism.

The NSA access was enabled by changes to US surveillance law introduced under President Bush and renewed under Obama in December 2012.

The program facilitates extensive, in-depth surveillance on live communications and stored information. The law allows for the targeting of any customers of participating firms who live outside the US, or those Americans whose communications include people outside the US.

It also opens the possibility of communications made entirely within the US being collected without warrants.

Disclosure of the Prism program follows a leak to the Guardian on Wednesday of a top-secret court order compelling telecoms provider Verizon to turn over the telephone records of millions of US customers.

The participation of the internet companies in Prism will add to the debate, ignited by the Verizon revelation, about the scale of surveillance by the intelligence services. Unlike the collection of those call records, this surveillance can include the content of communications and not just the metadata.

Some of the world's largest internet brands are claimed to be part of the information-sharing program since its introduction in 2007. Microsoft – which is currently running an advertising campaign with the slogan "Your privacy is our priority" – was the first, with collection beginning in December 2007.

It was followed by Yahoo in 2008; Google, Facebook and PalTalk in 2009; YouTube in 2010; Skype and AOL in 2011; and finally Apple, which joined the program in 2012. The program is continuing to expand, with other providers due to come online.

Collectively, the companies cover the vast majority of online email, search, video and communications networks.

The extent and nature of the data collected from each company varies.

Companies are legally obliged to comply with requests for users' communications under US law, but the Prism program allows the intelligence services direct acce