There are three ways to check open ports, the first being a port monitor for your PC, second a port sniffer and third, a remote security scan and here are the free applications you need.
An excellent port monitor is TCPview by Mark Russinovich which runs on Windows and will display any TCP and UDP ports open on your computer. It also shows you the address the port is connecting to, its status (listening, waiting or established) and more importantly, the file or program that has that port open.
The second way to check open ports is by using a port sniffer like Wireshark. This software, like that above, is 100% free and will show you the packets that are traveling across the network. It’s a great way to find out what your computer is sending and receiving, as well as other computers on the network.
The third way to check for open ports is to run our free firewall test. This is a view of your system from outside and can reveal some pretty alarming security holes. It’s also a great way to find out if you have your system locked down like you think you do.