How to determine what process has opened a network connection?
&gt; lsof -i :58199
COMMAND   PID USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
Transmiss 304 Fyodor    8u  IPv4 0x2fbc34fe135e3895      0t0  UDP *:58199


lsof = list open files. See manual for more details.

/usr/sbin/lsof


You can see with "ps -ef" more info about the PID "lsof" gave you.