It's basically a catch-22 situation, if you don't run a (good) virus checker you have no idea if you've got a virus or not. It's not like in the 90s where viru

It's basically a catch-22 situation, if you don't run a (good) virus checker you have no idea if you've got a virus or not. It's not like in the 90s where viruses would just destroy stuff and taunt users, modern viruses are often silent stealing data or turning machines into sleeper cells on bot networks. Viruses no longer rely on downloads to spread either (downloadable software is in a death spiral), they now commonly spread through zero-day exploits in browser software and extensions (flash, pdf readers, java, etc.) You don't have to visit dodgy sites either, many viruses are spread through legitimate ad networks or compromised web-servers (hacked wordpress installs are often used). Any software on your machine that handles data received from the outside world (including games, word, skype, etc.) is an attack vector. If you're not running a virus checker you're essentially just hoping you'll be lucky. Being careful will only take you part of the way.