Most viruses back in the day just slammed you with a billion popups and added suspicious files to certain areas of your file system. You could easily see if you were infected or not.
Also, in the past, I've on occasion scanned my machine using malware bytes and other tools and they always came up clean.
Of course that doesn't mean I'm in the clear but if an A / V tool doesn't detect it, then what point is there to run that A / V tool? Truthfully, it's really really easy to write a malicious tool and not have it be detected by any type of software. That's why you should be careful with downloading and running unknown software (which I am very careful of).
Also, in the past, I've on occasion scanned my machine using malware bytes and other tools and they always came up clean.
Of course that doesn't mean I'm in the clear but if an A / V tool doesn't detect it, then what point is there to run that A / V tool? Truthfully, it's really really easy to write a malicious tool and not have it be detected by any type of software. That's why you should be careful with downloading and running unknown software (which I am very careful of).