German officials have shut down a criminal web hosting service that was operating out of a former NATO bunker, according to a report from The Associated Press.

a Dutch man purchased bunker in 2013

According to the report, investigators tracked down a Dutch man who bought the bunker, based in western Germany, in 2013. The man had allegedly converted the bunker into a so-called “bulletproof” web hosting service, which was then used by illicit marketplaces for weed, synthetic drugs, and hacking tools. Investigators also reportedly linked the hosting service to a botnet attack on Deutsche Telekom.

The AP reports that seven people were arrested at a restaurant near Frankfurt in connection with the investigation, which also included raids that stretched across the Netherlands, Poland, and Luxembourg. Another six people are under investigation, according to the report, and authorities believe all of them are accessories to crimes related to drug distribution and counterfeiting money.

Bulletproof hosting services, like the one allegedly run out of the bunker, cater to criminals who want to outsource the work of hiding their digital activity. The work can be lucrative: in 2013, prosecutors said one provider was running more than 130 servers, in some cases charging more than 1,000 euros a month.

Running a service out a former NATO bunker, though, seems to be an escalation in security. Prosecutors declared the raids “a huge success,” according to the AP.