Let’s say you want to know which apps are accessing the net from your computer, especially if you think you've been infected by a virus. Windows comes with Netstat (you have to open it through the cmd>run as administrator), and then open task manager and then in task manager to view>select columns>check PID (process identifier) to get the PID number, and then open Fport (you have to download it first from McAfee) to be able to shut off the processes to delete suspicious apps.

Well, it’s actually MUCH easier than that with CurrPorts from NirSoft…and it’s free. It gives all open TCP/IP and UDP ports on your computer, the apps accessing them and info about the apps including the process name, full path of the process, version information of the process (product name, file description, and so on), the time that the process was created, and the user that created it.. I’d really recommend reading about it at the link above.

You can look up the suspect app (especially if it's on port 80 or the 400s) using http://spywareguide.com/

It’s really great because it’ll even outline any suspicious apps (with name) in pink, and allow you to turn them off from that window, generate reports, and has a whole bunch of switches for specialized commands which you can also access from the Help option.

So…here’s a screenie of what it looks like (from NirSoft.net):