McAfee is very good about not having false positives. However, it is sometimes also very good at not finding viruses and trojans. How can you know you truly have no viruses unless you have run another AV to double-check?
I agree. I have several anti-malware programs that I run from time to time. One of them, Malwarebytes Anti-Malware Pro, apparently will find all kinds of viruses, trojans, and other malware. It seems especially good at identifying stuff that slips by other AV and anti-malware programs.
Of course, another way you often can know that you have no viruses is that your computer doesn't do anything strange. Your firewall doesn't report strange programs attempting to call out, you don't get re-routed to other pages, your homepage is stable, your hosts file isn't tampered with, etc. etc.
I wouldn't get Avast. It's real-time monitoring interferes with too many programs, but maybe you should download a trial version of NOD32 or Kaspersky & give them a try?
Thanks for the advice. I think that's another reason I've kept McAfee: people have reported negative things about every other program I've thought about. Avast, Avira, NOD32, Kapersky, Bit Defender.... I do value your opinion highly, though, so I'll definitely keep your warning in mind.