If your network devices have default or weak passwords, attacker can change your DNS addresses (or worse, forward all traffic to its own network) to get and alter your DNS requests.

If TeamViewer VPN driver is installed and active, remote user can get in to your home network via using your computer as a bridge.If you are not careful he can install malware or change your teamviewer files with evil ones. However when the connection is established, you will see a pop-up window that lets you see what remote user viewing, copying or deleting. Remote user can connect your computer with File Transfer function.All you have to do is plug out your network cable or power cord, that will stop him. If required drivers are all installed (remote user can install that too) he can disable your screen and lock your keyboard to do dirty things without you seeing it but not without noticing it.

None of these functions have hidden mode and again none of them lets remote user view or manage your computer without you noticing it. They are Remote Control, File Transfer and VPN (if driver is available).

TeamViewer has three built-in functionalities to let user access to remote computer.

How to use teamviewer without wifi