In the past it was easy. Computers were offline.
Now we have to take care of computers, phones, and you heard it correct: even routers.
And if there is a modem between your router and the internet, think about having a good relationship with your modem also.
I found this website and I am shocked! We are all dealing with crypto currencies now and we'll be in trouble if we select poor modems/routers.
A compromised router can trick you and show you an attacker's crafted website while you are thinking you are interacting the good old website that you were visiting for a while.
What can happen? Bad things.
I'll quote his "What can go wrong" webpage.
Every bad thing you can imagine happening to a computing device, can happen to one that sits behind a hacked router. The only limit is the imagination of the bad guys."
I'll leave it to the expert:
I'll also shoot my own hyper paranoiac delusion. A hacked router can provide you an ISO for your brand new OS. You are thinking nothing can go wrong. Brand new OS. I won't install any crappy software. Guess what. It was hacked already from day 0.