Have you ever been RAT and how did you deal with it?

If you ever see someone else controlling your PC or something suspicious: Pull out the internet connection or turn it off completely.
If you're using a laptop, then either unplug the router, switch off the WiFi adapter or just pull out the battery and do 1 or 2.

Once you're done with that, get yourself an AntiVirus and try to get rid of it. If that doesn't work and you can't remove it manually, then reinstalling or restoring Windows is a good idea.
Protect your personal files over anything.