If during idling the computer actively interacts with the network, it does not update the operating system files, or antivirus databases, you need to find a program that uses traffic.
To start, try to find this program by means of the OS itself. Open a command prompt: start, All programs, Accessories, Command prompt. Type netstat —aon and press Enter. You will see a list of current connections. In the column "Status" in the currently active connection will be marked as Established.
In the next column – PID - specified process IDs. Knowing the identifier, you will be able to figure out what program is using the connection. In the same window, type and run the tasklist command, you will see a list of running processes. Immediately after the process name is the ID number. Look in this column the number you are interested in ID, to the left of it will be the name of the process program. In that case, if the name of the process mean nothing to you, type it into a search engine and you will get about all the necessary information.
To find out what specific program is using the traffic, start alternately to close suspicious active processes that have a connection to the network. To stop the processes in task Manager (Ctrl + Alt + Del) or directly on the command line, using command: taskkill /pid 1234 where 1234 is the process ID that should be closed (it will have others). If after the closing process, the traffic dropped, then you have found your desired program. If not, close following, etc.
You can exercise more complete control over the traffic using BWmeter. Find it on the Internet, download and run, then open the Details tab. Locate the Control panel, press the Start button. In the window of the program will display information for all ip addresses, with which is connected the computer.
To monitor network activity use AnVir Task Manager. It allows you to see all network connections and find the use of their program. With this utility you will be able to find in the registry and the keys you are interested in running any of the programs and, if necessary, to remove them.