Belt-and-braces are a good approach for most things (like trousers) but not with Antivirus products.I’ve heard some people suggesting having two Antivirus programs is good for additional protection. Wrong! Doing this intentionally is a bad idea, but it also happens unwittingly sometimes, and here is why:
Antivirus software works by scanning files as they are accessed or created; keeping an eye out for new files that you might download, save or modify and then scans them for malware. If anything suspect is found in the file then it is quarantined or deleted.
The act of scanning a file for malware also modifies the file slightly, but the antivirus software doesn’t bother scanning the file again, because it knows that it has only just scanned it.
Let’s imagine that you’ve somehow managed to get two antivirus programs installed: You save a file which is scanned by program A. Program A finds nothing, but the act of scanning it changes the file slightly. Program B then sees that change and scans it, finds nothing, but still changes the file slightly. Program A then sees the second file change, and scans it again, finds nothing but still changes the file slightly. Program B then sees…. Well you get the idea.
Your machine will work fine for the first few minutes but then grinds to a halt because of the thousands of files stuck in a circular scanning loop.
Windows Defender is built into Windows 10. This is good for very basic use like browsing and email, but it is good advice to have a premium antivirus product like McAfee if you do any online banking, shopping or store sensitive data. When you install a 3rd party antivirus product Windows Defender will automatically be disabled, but sometimes this doesn’t happen and you can have Windows defender and your 3rd party product fighting against each other.
Sometimes people change antivirus providers but fail to remove the old product first. Sometimes the old product doesn’t uninstall cleanly and leaves active remnants. Sometimes your new computer can come with a trial version of a product that remains on the computer after you’ve installed your own subscription. Sometimes antimalware tools like MalwareBytes, CCleaner or Spybot can clash with your live antivirus program. If you have a poorly performing Mac or PC then check first to see if you have multiple antivirus products.