North Korea orchestrated a long-running, large-scale computer hacking operation against South Korean companies, police in Seoul said Monday.

Blueprints and specifications for a U.S. fighter jet were stolen as part of a haul that included more than 42,000 documents, according to Reuters.

“There is a high possibility that the North aimed to cause confusion on a national scale by launching a simultaneous attack after securing many targets of cyber terror, or intended to continuously steal industrial and military secrets,” Seoul’s Cyber Terror Response Center (CTRC) said.

Many of the documents were stolen from the South Korean conglomerates SK and Hanjin.