My opinion:
Anti-virus is close to useless these days, or rather - beginning Windows 7, the built-in defender is totally sufficient.
However, you need to make sure you use a good anti-malware, you have correctly set Firewall and most importantly ! you dont click and open everything you see - in such case even the best AV or FW will not help you.
The problem with AV is that most are not very reliable anyway (or rather I should say not much better than the built-in one) and they are probably the most slowing down SW you can install on your PC.
The other issue is that some people even install more AV on one PC
What also makes this dangerous is that they then assume - "oh, no problems, Im totally protected, I can do anything, if it is a virus, I will be told" - which obviously is wrong.
Oh... and btw..... half a yr ago I saved our company.... I was at work, Friday late afternoon when I suddenly noticed very strange things going on on our network drives. Because I do lot of IT stuff in my company too I have admin rights on my PC and I installed some additional security SW, in addition to the one we all have to use.
I quickly realized what happened - someone's personal laptop got infected, they connected the laptop to our network to access some files, the virus (ransomware...) "jumped" to the network drives and started encrypting everything, every network shared drive and jumped to all PCs that were currently online (I was there by myself it was late on Friday, but many people leave their PCs on over weekend because they do all sorts of calculations and so they wont even notice the slow behavior!)
I immediately called our IT manager, he was there within an hour, we completely disconnected everything (even the forecast servers
). We then had to find the computer that was spreading this. Then going through all offices, checking all PCs that were on... when I went home at 3.30AM we managed to stop it from spreading. Next morning and on Sunday I fortunately found a SW that could decrypt it, but not everything, it only worked for about 80% of the files, rest was lost.
We did have a backup of all this, but it is only made once every month because it is too big. I dont even want to think what would happen if I didnt notice and the thing was spreading and slowly encrypting everything the whole weekend...