Need Urgent Help

Hi Friends,
I have a problem in my office, that is reporting a heavy upload & download traffic in my ISA server, i think some unidentified application increasing upload traffic, as usual our usage was 8 GB per month now it has increased to 45GB, how can I identify & block process, please let me know what would be the solution.

Regards
BYJU
IT OFFICER
EHSAL EUROPEAN UNIVERSITY