Germany's Federal Intelligence Service BND has allegedly been spying on European politicians and businesses on behalf of the NSA for over a decade.
Der Spiegel reports that for years the NSA collaborated with its counterparts in Germany, collecting data from thousands of targets.
German cyber-spies fed this data into their own surveillance systems. The reports generated were evaluated by the BND before being passed back to the NSA.
On a practical level, it appears that the BND has had access to and monitored Frankfurt's Internet Exchange Point DE-CIX since at least 2009.
The results of these mass surveillances were transferred, at least in part, to the Americans as part of a collective agreement that existed between the two services.
Targets included European politicians and European aerospace and defense companies, such as the European Aeronautic Defence and Space Company (EADS) and Eurocopter.
So far so good with the spying cooperation.
BND employees collected data from these strange targets (which had nothing to do with those mentioned in the US-Germany bilateral agreement signed in 2002) without complaint, at least until 2008. The US-Germany bilateral agreement was intended to focus the efforts of the two agencies on combating global terrorism.
However, it was only when Edward Snowden's revelations came to light in 2013 that the German intelligence service began to question the practice, which had more of a profile of economic espionage.
It is estimated that around 800,000 selected requests passed from the NSA to the BND in total during their collaboration. An internal probe following the Edward Snowden revelations concluded that at least 2,000 of these spying requests were against German or wider EU interests.
The BND helped the NSA spy on European ministers and businesses, without anyone in the German parliament knowing.
The BND Administration did not convey the agency's findings to the Prime Minister's office, simply asking the NSA not to filter requests that were potentially contrary to German political and economic interests.
Once the German parliament was informed of the NSA's actions, the BND was asked to review its data, before concluding that around 40,000 targets were directed against the interests of the EU and Germany.
The report issued by the BND on the practices they followed has once again sparked a huge political debate about espionage in Germany, as reported by De Welt.
The dispute risks torpedoing already strained relations between Berlin and Washington. Germany is still in the process of healing its wounds from revelations last year that the NSA was mass-spying German citizens and tapping data from German Chancellor Angela Merkel's cellphone.
