Malwarebytes MBAM, and other similar, 'find' and try to eliminate viruses once the machine is infected.
It is probably easy to write a virus to disable programs like this, though.
I've seen a number of cases where AV software was quite obviously crippled by some trojan.
I've never caught anything but my kids have; my teenage son was once found to have 13 trojans on his laptop. Now he doesn't allow anybody to look at his laptop (due to top secret Facebook etc communications) so I have banned him from internet connectivity at home, allowing him to access the web only via a specially configured AP which blocks all ports except 80, 443 and 59 I think (DNS). Normally he lives with my ex who doesn't care what he does
I think installing AV software on a machine in that condition, infected by relatively recent viruses, may be a partly wasted exercise.