Help Instant data usage stats for different apps individually

[zaa sala]

There was a sudden increase in the download speed which is being displaed in the notifications bar. I want to check which app is causing that.
Is there any way to check the instantaneous data download stats and by which app.

 

[ocnbrze]

Increase in download speed? From an app? Isn't that a good thing? Why do you need to know? Never have I come across such a thing.

Edit: I just googled "android app monitor data usage" and found quite a few hits.