why ? Another user is trying to view my ubuntu desktop

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http://stackoverflow.com – Yesterday,when I was using Ubuntu, I encountered a shocking message that I am very confused about. The message said: "Another user is trying to view your desktop. A user on the computer ********** is trying to remotely view or control the desktop. Allow? Deny?" My computer only had the root account enabled, (with a complicated password); I also enabled a VNC Server on my computer. I inspected my '/etc/passwd', but there was not a new and unfamiliar account. I chose to deny it, but I don't exactly what does this mean. Therefore, I am concerned about this. Any help would be greatly appre (HowTos)