Just do not click or download anything fishy,
Thats the thing- HOW do you know whats "fishy"? Good sites can be hijacked through ads! People have had virus alerts even from this site in the past.
This simply means that gamedev is also a fishy site, don't mix what you'd consider fishy for browsing and what's fishy for running code on your computer, only download programs from their own websites, if you need to download maya demo, download it from autodesk's website, if you need to download avast, download it from avast's website, if you need to download visual studio follow links from Microsoft.com etc, that's the easiest way not to download crap, additionally if you want to be safe don't run any unsigned installer or installers signed by a company other than the one the product is from.
The thing is you don't even need to download "fishy" Malware. Lenovo, Dell and Toshiba have all been stung in the past for selling brand new laptops that have had pre installed bloatware that was already infected.
Don't mix bloatware with virus here, typically stuff you don't need comes preinstalled in demo versions yes, it's a tradeoff, it's also what makes decent computers so cheap, if you don't want of it you simply reinstall a clean Windows over or uninstall them, but this has nothing to do with antiviruses which is the topic's title, specially since in most case there's at least 1 antivirus in the bundle. . .