Where are your computer connected?
In the Windows you can use the netstat command in command prompt. It will provide a list of all the programs are using Internet connection in a given time period.
First you need to run the command prompt with admin rights. From your Start menu, type "cmd" in the search box. You will see cmd.exe program, right-click to the program and select "Run as administrator".
User Account Control dialog box asking for confirmation appear. select Yes.
In the command prompt screen, type the following command and press Enter:
netstat -abf 5 > activity.txt
The options -a displays all connections and ports waiting for connection. The option -b tell you about applications are connected, and -f will show every connections. We can know where are the connections exists. You can use -n option if you want to show IP Address that connections go to. The 5 param in the statement means every 5 seconds, the program will repeat the test once and the results will be stored in a text file activity.txt. Wait around 2 minutes, then press Ctrl + C to stop the command.
After completed, let open the activity.txt in any Text Editor program. This content file are all processes on your computer (such as browsers, email programs, chat ...) which connected to the Internet within two minutes running netstat command.
If you see any unknown process or the name, please search information about it on Google. Maybe it is a system process, but it can be also virus, spyware ... If you doubt it, searching for informations, ask on the forum for sure.
Using CurrPorts to check the hidden connections
You can also use a free software called CurrPorts. This program offers a user-friendly interface allows you to view all connected TCP / IP and UDP ports are open on your computer. CurrPorts is a portable program, you do not need to install to use. Download the program HERE.
I just mentioned two simplest ways help you checking for hidden connections in your Windows.