network usage problem

[munshi]

hello,
i have an imac 21' with OS 10.5 leopard and all the updates installed and everything is supposed to be running smoothly.and i use the iStat pro to track everything.
a week ago, i noticed something really strange. something is downloading on my computer and eating all the bandwidth to the extent i can't even browse the internet😕. i quit all the programs running but still it was not faltering. the only thing that seemed to work is to turn off airport and turning it on again, is there any other way to know what is doing that to me and how to stop it.
i read somewhere about littlesnitch but it did not help me. any suggesstions on what does this and how to manage it?

 

[slpdLoad]

Is Software Update set to download updates automatically in the background?

 

[munshi]

i have thought of that first and i did a manual check for update and nothing is available for me.so its not the software update...

 

[phatqao]

use Applications/Utilities/Activity Monitor to see if you have any processes eating up a lot of CPU time