Prior to Windows 2000 there was no built-in possibility to figure out which program on your system opened which port. You could use ‘netstat -an’ to list all open ports, but not which process or library has opened the ports. TcpView from SysInternals came to a rescue.

Starting with Windows XP and 2003 ‘netstat -ano’ shows the ID of the process that opened the port. So you could modify your task manager view to include PIDs and figure it out that way.

XP SP2 adds new switches to netstat to directly show the program (plus the subcomponents) that opened the port. cool.

try ‘netstat -b’ for a overview and ‘netstat -bv’ for more detailed info.

I still can recommend TcpView and for the highest possible amount of in-sight use Process Explorer (which can even replace the task manager).