Many are killed in falls or by heart attacks or endemic disease, one expert says.
Installing the 'Red Star' operating system and solving information technology problems puts money in the pockets of the technologically savvy.
Authorities are no longer letting residents obtain documents to travel to China to visit family members or conduct private business.
The soldiers, who are told to disguise their identity, are increasingly replacing North Korean civilians sent abroad to work.
The new procedure allows firms and factories to conduct transactions without relying on promissory notes.
Meanwhile, security officers travel with larger vessels to monitor crews' use of communications equipment.