iMac downloading a lot off the net

My imac seems to be downloading a fortune of data from the internet, I an using a program SurplusMeter which is telling me how much data is being downloaded, however is there a program that I can use to tell me which of my application is downloading the data or how can I tell what is causing these large downloads.

Regards

Antony

Take a look at which apps are actively running, then open up Activity Monitor and see which apps are running there..and what is a fortune of data? As long as you are connected to the Internet, there will always be some amount of downloading going on..

SurplusMeter measures all outgoing and incoming traffic regardless of where it's going. For instance, if you share a 2GB file across a home network, SM doesn't differentiate this from outgoing HTTP traffic (the former of course not counting as outgoing traffic in terms of the plan you have with your ISP). Therefore, the results it presents can be deceiving. Do you share/stream any data to/from your Mac within a home network?