Security Question

You need antivirus if even one of the following is true for you.

Your PC is connected to the internet.
Your PC is connected to a network where other PCs are connected to the internet.
Your PC has USB port which you connect your USB stick, which is also used on other PCs.
Your PC has a CD/DVD/Bluray Drive that you use.
Your PC has external drive that is also used on other PCs.

If you are looking at this post on your PC, it means you need an antivirus, even if you are a boss level computer genius. Don't listen to people who say you don't need an antivirus that actively scans what's going on in the background. If you deal with files, any files, the internet is like a wild place. Software like MalwareBytes is great and all but by the time you suspect something is wrong with your system, it's already too late. I agree that some antivirus software won't catch all of the viruses trying to penetrate, it's still worth having it than nothing at all.

If I ran a massive botnet, I'd love people who don't use antivirus. Can't wait to get your PC as part of my bot herd.
If I was "release group" with pink or green skull on TPB, I'd just slip a Trojan or a worm or a rootkit and you won't even notice a thing since you don't have an antivirus actively scanning incoming files. Yea I will lose my status on TPB but i still have your system part of my herd and you probably don't suspect a thing until you visit the same release and check comments from people who actually use antiviruses.

You'll say that you check the files you download against a checksum SHA-1 or MD5. These can be faked.

Let's say you really need an awesome looking game mod (e.g. https://hellclan.co.uk/threads/37280/) for your favourite game, you download the zip file and upon extracting, it's an executable file.
What if upon executing this file, all of your data starts encrypting and then it asks you to pay before they will send you the key to decrypt your own data? BTW, don't pay a penny, they want you to pay in bitcoins and they won't send you anything back. Format your PC and deal with not having an antivirus.

You can get infected just by visiting certain websites... even if you are sure a website is safe, has valid certificates etc, it can get hacked and be made to infect it's visitors. You cant blame the website owner, you are in charge of securing your system.

The situation can be so grim that if a worm has many unpatched zero-days, there is no escaping it, even with an antivirus. Mostly governments do shit like this, and it could be some corrupt dictatorial government not necessarily your own.