Wow! This is something new to me, and it is a bit technical. How does someone who is not familiar with the technicalities detect this hole?
The simplest solution to avoid it entirely is probably to set a static DNS for your computer. Google's (8.8.8.8 or 8.8.4.4) should be good enough for most, but you may want to look up Open DNS or other providers. This is pretty easy to do, you just need to Google exact instructions for your OS.
You can otherwise tweak your router to detect it, but that requires a bit more technical knowledge. If you're suspicious of the person who installed it, you can just do a factory reset to undo whatever he modified -- this may break your connection depending on the ISP though, so be careful.
VPNs also work. Everyone who uses crypto should have a VPN imo.