You can probably run (within a command prompt) netstat -a which will show all active connections to and from your computer. If you want a GUI version of the command, you can go to CNet’s Download.com Portal, and download “Active Ports”. It does the same thing and in addition you can run a nslookup and terminate connection.
You can also right click on My Computer. select System Tools, Shared Folders, Shares and see who is connected to the default shares like Admin$, IPC$ or C$
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