@DrVarunMehta, you can use
DUMeter (
www.dumeter.com) for monitoring
the Net activity. There may be several causes for your problem.
1) Automatic Updates
2) Malicious activity of a Spyware / Adware
Better use ZoneAlarm firewall & configure it. Also don't use IE browser. Since all
these Spywares use IE to connect to the Net!!!. You can use FireFox or Opera.
Also don't visit untrusted websites. With ZoneAlarm , you can allow/deny & monitor
which programs connect to the Net. Also it's easy to configure & the best firewall.