That you know of. For all you know you could be infected and part of a botnet. Viruses don't open a big popup saying "haha you've been hacked!".
This line of thinking is extremely common and absolutely nonsensical. The point of a virus is to remain undetected.
Most malware these days does things like demand bitcoin, popup ads, or upload your files to the cloud without your consent.
If I've actually unknowingly downloaded a virus, it's honestly less malevolent than the paid version.
This is a remarkable observation on the sad state of paid software. It's so sad because it's so true.
I don't mind buying software, but I do mind pretty much all DRM implementations. Even simple license checks have bitten me in the past when I had no internet access and the software just decided that time was up and it needed to verify me. Nothing fills me with rage more than software that I paid for refusing to run while I'm camping or on a plane or somewhere else without internet, for software that doesn't need any networt functionality whatsoever to operate.
If a tree falls in a forest and no one is around to hear it, does it make a sound?