As I spent a recent two days figuring out how someone from Han Hoi Precision Ind. Co. Ltd. had a local IP address on my network and getting it cleaned up. During that time I found the Secure DNS feature going on-and-off without cause. (not cycling quickly). After everything was cleaned and verified, the Secure DNS feature was on and working. Then a few hours later, it was off again. After verifying I wasn't under attack and everything was stable, it went on again. And now it's off again.
I found the device injected into my network by running the Avast 'Scan for network threats' and if not for that feature, I may have never found the intruder. That said though, the person probably got in because the Secure DNS feature is inconsistent.
If Avast doesn't at least post a response to these concerns soon, I'm going to have to assume they're not so good at this home network security thing.