Since they have access to the PC as a whole, it's on your LAN so they can install anything and create havoc.
See if your router has a Guest Access mode to place this machine in it's own network for safety. Then you can explore remote access with VNC or other apps.
Bob
I'm looking for the best way to give an outsourced worker access to my computer. I have an extra computer so I'm not worried about any of the files on the computer. The worker will need to have internet access in order to log in to a website and do some research. What's an economical/safe way to give them access to my computer/internet without compromising any of the computers that also use the same internet?
Thanks

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic