The recent high-profile arrests of alleged China and Russia spies in Germany highlight the extent of hostile foreign infiltration in the country. The extent of this infiltration is in part a legacy of political "naivety" that followed the end of the Cold War, says Roderich Kiesewetter, a former German Army officer who is now an opposition MP, who alleged China was seeking to gain access to advanced research that could be useful for military or other purposes.

"Since 1990, there was the idea that Germany is surrounded by friends", he says.

Leaders were focused on business deals, including with autocratic countries such as Russia, and took their eye off national security, he explained.

Rafael Loss of the European Council on Foreign Relations is more specific about what went wrong.

German intelligence entirely wound down a unit dedicated to counter-intelligence in 2002 under Chancellor Gerhard Schröder.

"It is remarkable that this entire unit of roughly 60 people was completely disbanded," Mr Loss says.

But things are changing. The BfV's staffing has doubled in the past 10 years. The recent spate of detentions shows that the intelligence services are becoming more assertive in a country whose political culture has traditionally been wary of them.

"All the arrests at once send a good signal to the nations that spy on us," said Felix Neumann of the Konrad Adenauer Foundation. "Germany is awake and not asleep any more."