Germany’s domestic spy agency told companies on Wednesday they should be on guard against industrial espionage by Beijing, warning them not to be naive or over-reliant on China.

The warning from the agency’s deputy head Sinan Selen came days after three German nationals were arrested on suspicion of handing over technology with military applications — a case which has highlighted mounting anxiety across western Europe about Chinese spying.

Germany is seen as particularly under threat due to its strong industrial sector and good business relations with China, its top trade partner. Chancellor Olaf Scholz visited China just 10 days ago.

The government has urged companies to reduce their risk exposure to China, the world’s second-largest economy, but critics say many still focus on short-term profit over long-term strategy.

“I think we are on a journey from a very naive and highly optimistic attitude towards other economic partners to a more realistic, perhaps more resilient and diversified attitude when it comes to partnerships and protecting Germany as a business location,” Selen said.