I use socket.io 0.9.6, and I get many logs client not handshaken client should reconnect from real users, but I could never reproduce it myself.
I tried many browsers (IE8-9, FF3.6-13, Chrome, Opera 11), I tried simulating high pings (up to 4s), but nothing to do, I never get this log.
What can I do to reproduce this ?
This may be caused by antivirus software or firewall on the client side. I had the same problem with avast antivirus.
Possible solution: Use several commonly known ports such as 80, 25, 443, 843, 110, 5190, 5222, 5223, etc. using port forwarding on the server side. If connection fails on client side, try to change port and connect again. It works for me.