We sometimes need to figure out whats running on our computers that have created connections for the outside world. The needs could be for check if you have any ad ware / trojans. The other reason is when we ourselves want to know if a certain program is running properly or what port it is listening too or figure out which system has connected into your machine.
There is this built in program in Dos called netstat but its very very basic and works only in the dos prompt. As always there is a lovely little stand alone program that is part of the sysinternal suite called tcpview. t doesn't need to be installed and has a zero footprint.
It shows all the application on your PC / Server that have open connection / established conections and the ports that are getting used. It also has a setting whereby you set the refresh time to update the current connections.
Sysinternals got bought over by Microsoft and now is hosted at microsoft
Hope this has helped you out. Do drop me a line !