How do I monitor network activity on my Mac 10.6?

Question

I need to know which applications are accessing the internet on my Mac. I want to know how much data they uploaded and downloaded. I got a steep 3G bill this month because some stupid app is downloading something in the background, and I don't know what it is.

All I need to do, is find it, and block it, or turn it off.

Can anyone please help?

Answer 1

Try Little Snitch

A firewall protects your computer against unwanted guests 
from the Internet. But who protects your private data from 
being sent out? Little Snitch does!