The first idea of writing a packet sniffer program came from a reply to my comments on one of the projects named NetSend ( Sending popup messenger messages between computers ) by Marc Clifton. Marc asked me What about receiving message. To say the truth, I didn't know how I could do that. I knew a program which I had downloaded and tested years ago. But I didnt know the way of it. So I made a search on net about programs that can receive messages created by NetSend. And I noticed that many of them were using packet sniffer libraries. And then decided to learn how it is done. My search attempts gave a result and I found a free library named WinPCap.