How can I quickly find listening/open ports on my computer ?

You can use the NETSTAT command to quickly see all the used and listening ports on your computer. Note it is not a complete substitute for a port scanning tool. If you'd like to have your computer remotely scanned for open ports use our Security Scan instead.

To see a list of listening ports, open Command Prompt and type:

C:\> netstat -an |find /i "listening"

You can change "listening" to "established" to see what ports your computer actually communicates with.

It is also useful to use the -o switch with the NETSTAT command to also get a list of all the owning process ID associated with each connection. You can then use those process ids (PIDs) to find out the name of the processes associated with open/listening ports in the Windows Task Manager

C:\> netstat -ao |find /i "listening"

To see all open, closing, established and listening ports, simply use:

C:\> netstat -a (or netstat -ao in XP/Win2k3)

You can also make the netstat command refresh periodically by adding a number of seconds at the end, for example, to make it refresh every 5 seconds, use something like:

C:\> netstat -an 5


Notes:
The netstat command has a number of other useful command line parameters, you can see short description of all of them using: netstat /?
Also, you might want to perform an outside port scan to see what ports are accepting connections according to an external machine. See: SG Security Scan
You can see process identifiers using the following command at the command prompt: tasklist and tasklist /svc