No I cannot open these PC, access not granted or a psswd is required.
But I think I discovered the root cause of this:
My son, playing online minecraft, has installed a program called "LogMeIn Hamachi" and these mentioned PC are listed in this program under others. When these PCs are "online" in LogMEIn Hamachi, my PC see them under "Network"
I do not know what this program is for and what threat it is for security. Any idea, comment?
Thank you for all replies so far, I appreciate.