In order to obtain a copy of the NSA’s main XKeyscore software, whose existence was first revealed by Edward Snowden in 2013, Germany’s domestic intelligence agency agreed to hand over metadata of German citizens it spies on. According to documents seen by the German newspaper Die Zeit, after 18 months of negotiations, the US and Germany signed an agreement in April 2013 that would allow the Federal Office for the Protection of the Constitution (Bundesamtes für Verfassungsschutz—BfV) to obtain a copy of the NSA’s most important program and to adopt it for the analysis of data gathered in Germany.
Source: Germany trades citizens’ metadata for NSA’s top spy software | Ars Technica