That's not all they've been sending over - those thumb drives are also loaded with porn, anime and spyware ofc. They were even running temporary meshnetworks with them to eavesdrop on cell networks at one point.

The North Koreans have also been sending back more than just rubbish. A lot of literal shit, human and animal has made it's way across the DMZ over the years. 

This has been going on for almost a decade, I wonder why it's a news story now? 

 I wonder too, especially since its been going on for several decades. Both sides started doing that right after the war. I think they stopped for a period, though.