Sudden increase in outgoing traffic

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http://serverfault.com – My server is witnessing a sudden increase in traffic. Consistently there is a 200mb outgoing traffic every hour. This is not my web traffic. I am running centos OS and completely new to server administration. Can some one help me to figure out what is causing the traffic. I tried all possible netstat lsof etc. But couldnt really figure out what is causing this. Since my bandwidth is limited this is causing a real headache. Any help on this front will be useful. (HowTos)