Screen Sharing Security

Do you mean you System Preferences -> Sharing -> Screen Sharing -> Computer Settings -> VNC viewers may control screen with password ???

If you are going to use another Mac, then you do not need to set the VNC password, since other Macs can use your account's username and password.

The VNC password is for 3rd party VNC clients, and VNC clients coming from non-Mac systems.

If your Mac stays behind a home router, AND you do NOT open "Port Forward" port 5900 from the internet to your Mac, then ONLY your home systems can use screen sharing.

If you take your Mac out of the house and into public WiFi access points, then a potential stranger can attempt to connect to your Mac's screen sharing. So you should have a very good password.

Mac to Mac screen sharing, using the username/password, is done in a secure manor.

Using a VNC client and the "VNC viewers may control screen with password" is not secure. If done at home behind your home router, no problem.

If you make a screen sharing connection in a Public WiFi location using the "VNC viewers may control screen with password" then someone could sniff your connection attempt and obtain your "VNC viewers may control screen with password" password.

As for turning off screen sharing when not using it, as long as your have a strong password for both your "VNC viewers may control screen with password" value and for your Account/Password, AND you do not make a connection where a Public WiFi could steal your "VNC viewers may control screen with password" value, then it is unlikely someone will guess the needed password information so they could get into your system.

You may have also answered my question, but I'd like to confirm this with you. I have an iMac behind a home router (Airport extreme base station) and I have configured the base station using Port mapping 548->local IP address:548 (using Airport Utility/Manual Setup/Advanced/Port Mapping) so that I can access the files on the hard drive of that home computer from my work computer (also an iMac). That part works fine. However, I have been unsuccessful at getting screen sharing to work either from home to work or from work to home. (I have confirmed that both are checked in the System Preferences.) Are you saying I should add another Port Mapping command using port 5900 so that screen sharing will be activated; i.e. put in 5900->local IP address:5900 in addition to the 598 port mapping command?

Yes, as Screen Sharing uses port 5900 and not 548, you do need to open a port just for Screen Sharing.

NOTE: Since the original post was about Screen Sharing security, by default your screen sharing (and your file sharing) are not secure. Screen Sharing, once you have started a session can be encrypted via an option in the Screen Sharing application on the client. I do not know of any way to make your file sharing secure, without tunneling over ssh or establishing a VPN connection (such as via MobileMe Back-to-my-Mac). If you wish to pursure secure connections further, you should start your own thread, or search for solutions previously posted.

By the way, you should really start your own thread when asking questions, as only the person starting thread can give "Stars" and points for Solved and Helpful answers. Since everyone that posts here is unpaid, points and stars are all they have to look forward to 🙂

I would say your set up is just fine as it is.

Port Forwarding is something you would have to manually configure on your home router. You would remember if you had done it.

Thanks Bob. I'll take your advice about screen sharing and also starting new threads. Best wishes.