Getting your computer attacked by a virus is a bit like catching the flu.
You can go years without catching one and then get two or three in one year.
My sister never had an antivirus on her computer for about 8 years.
She then rang me up and said it was running a bit slow and asked me to fix it.
I knew it didn't have an antivirus so I said it was probably full of viruses and worms and dung beetles and possibly even kangaroo ticks.
(Why not? What would she know?)
Anyway, I offered to pull the hard drive out and connect it to my machine and do a virus scan.
After more than 8 years on the internet, not even one virus!
It did have the usual truckload of tracking cookies and stuff that Norton finds and deletes every time it does a scan, just so that it can joyfully present the results to you with all the expectations of approval that your dog has when it drops the rotted out shell of a long dead bird or lizzard on the kitchen floor.

It was just running slow because the hard drive was chocka-block full.
Anyway, a bit later someone else was setting up their computer and asked if she should get an antivirus. I related what I just said above so she decided to just go with AVG, a free one off the internet.
A few months later the whole thing crashed because of some bug that AVG didn't pick up.
I put Norton on it and that fixed it up.
I run Norton on my compuda but I don't like it much.
I think it slows down access to some sites while it goes away and checks for birth certificates or a Standard and Poors rating or something.
I sometimes just give up.