Last year, when Avast added its Hardened mode to its antivirus software, the default was to have it disabled. You had to go into the software to enable it. I don’t know if that’s still the case, so just something to be aware of.
I’ve had the Aggressive option, which is cloud-based whitelisting, enabled for a year on Windows XP Pro without any problems. To enable it, go to Settings > General.
For more information about Hardened mode, see this Avast forum post: https://forum.avast.com/index.php?topic=142172.msg1032485#msg1032485
