Ive noticed over the last few weeks rather than getting an advert Im getting something along the lines of: 

\",\"id\": 486673124,\"custom\":{}}"),'native-5863945454448509294');

Its not any one in particular, the numbers change.  And its not always.  Its not limited to any particular area either, sometimes its the top banner, the bottom floating and the one inbetween forum posts. It can be a combination of one or all on the same page.  

An example (from just now) is: