Why is it that every computer i download minecraft on gets a virus?

Pay for it. Don't download mods (unless you know how to do it). And download it off the official website. If you do all that you shouldn't have a problem.

I did pay for it on the official website

Need better antivirus lol. I've installed it for multiple friends with no problems at all.

I have no idea why, but it's got nothing to do with Minecraft and more to do with whatever else you're doing on your computer.

The legitimate minecraft has no viruses. I'm guessing you're downloading cracked versions off some pirating site.