My Firewall is not letting me change permissions, and documents with .501 and .503 extensions are getting created related to Device Discovery and Image Capture!

I have good reason to believe my system has been compromised. Just a few minutes ago I went into the "System & Security" from the "Preferences" and I just happened to click on my firewall settings and in the window in which users can "allow" or "block" certain actions I saw a permission for screen sharing green and allowed, [shown in the picture below] and I tried many times to click on it and press the minus sign or change the permission from green to yellow or red and simply block it, but it appears to be frozen or locked and I cannot even select it. I'm on the administrator account so it's not a matter of user account. Clicking on it doesn't do anything. Having said that I can check and select the "Stealth Mode" and "Block All incoming Connections"... but why am I not able to select that Screen Sharing and what is it? [Image below]

I also spotted 2 strange looking docs created in my Library/Caches folder, file name: com.apple.ImageCaptureNotifications.DeviceDiscoveryDatabase.501 and com.apple.ImageCaptureNotifications.DeviceDiscoveryDatabase.503 [Image below]

In Finder, on the sidebar, next to the "Computer" icon under the devices, the title "Computer" itself has disappeared, and it's basicly blank and empty in front of the "Computer" Icon, it works and takes me to "Macintosh HD" when I click on it, but the writings have disappeared... [Image below]

Would anyone please tell me what this is all about? I'd really appreciate your help. Mac OS X 10.7.5 2.3 GHz Intel Core i7