I will lead you through a 3 step process that takes 30 seconds, and can save you $Hundreds of dollars in computer repair.
: Go under "Extras" in the top tab, and press "Options"
: You should have a box like the picture shown below, press the "Security" button the left side of the box, and on the bottom of the box it should say "Access Control", change it to "Custom Settings". Then press "Configure" (Make sure you press the right configure button, the one that is wrapped around in a blue box on my picture below is the one you're supposed to click."
: Now after you have pressed the "Configure" button, it should pop up another box like the picture I have below. Go to "File Transfer", and click on the scroll down box, and make it "Denied" or "After Confirmation"; what this does is if you are buying something such as a runescape membership pin, the seller cannot send you files that could possibly harm your computer or either the file will have to be confirmed by you, the buyer. Now press "OK", and your teamviewer should be safe!
Now you should be a step safer from any trojans or other virus files on your computer! If you chose the option "After Confirmation" in Step 3, just be smart when someone sends you a file, that it's not a virus file.
This guide was NOT made by me, It was made by Vanmaster5, i just made this thread for this section to help others stay safe.