The three providers in question are Stellar, Cetel and IABG, which operate satellite ground stations that provides Internet and telephone services to remote places such foreign outposts of business, political and non-governmental organizations.
According to Der Spiegel, the operation was conducted from a listening station in Cornwall, and targeted both the employees (mostly engineers) and the networks of those companies. Among the spied on individuals is apparently also Stellar CEO Christian Steffen.
The spies were also after information about the firms' customers. In Stellar's case, they are ISPs, telecoms and several governments; Cetel serves organizations in Africa and the Middle East, and provides Internet connectivity to diplomatic outposts of a northern European country; and IABG does business with the German government, its armed forces, and companies in the aerospace industry.
Another document reveals that the NSA targeted for surveillance 122 high-profile individuals - mostly presidents and government leaders around the world - including Angela Merkel, Syrian President Bashar al-Assad, (then) Ukrainian PM Yuliya Tymoshenko, and so on.
The information about these targets is collected via a system called Nymrod, which, according to The Intercept, "sifts through secret reports based on intercepted communications as well as full transcripts of faxes, phone calls, and communications collected from computer systems."
Other documents reveal that the US Foreign Intelligence Surveillance Court authorized the NSA to intercept communications related to a number of countries including Germany, China, Mexico, Brazil, Russia, and many more with the help of US telecomms like AT&T and Verizon, and Internet companies such as Google.
"The documents do not provide sufficient information to precisely determine the types of data included in the order, and the NSA has said it will not comment on the matter. However, lawyers at the American Civil Liberties Union believe it provides the NSA with permission to access the communications of all German citizens, regardless whether those affected are suspected of having committed an offense or not," Der Spiegel comments the FISA court order that allowed the monitoring of "Germany".
"Under the FISA Amendments Act, the NSA is permitted to conduct blanket surveillance in foreign countries without any requirement to submit individual cases for review by the court, whose deliberations and rulings are top secret."