How to find out which process is sending huge data to the internet? I have installed MenuMeters so I can see the realtime outbound date, sometimes it will display "out: 5xxKB/s" for a long time, so I want to know which process is sending data to the internet?

How to do that in Mac?
Activity Monitor


  Activity Monitor measures how resources are being used by different processes (or applications) on a Macintosh. 
  This can then be used to monitor the Mac's processor and disk activity, as well as the memory usage and network activity.



Open Activity Monitor (you can find it in Applications/Utilities)
Select 'Network' tab
Sort on sending or receiving data