How can you tell what your computer is doing on the net? Netstat. This handy program comes with almost all operating systems. On Windows, click Start, then select Command Prompt from the Programs->Accessories menu. To run Netstat, type netstat at the command prompt. For more readable output type netstat -ab.
Full documentation for the Windows version is online at Microsoft.com. On OS X or Linux, type man netstat at the command prompt.
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