How to enable/disable Secure DNS protection
Avast Antivirus 2015 has introduced a new feature against DNS hijacking, which forces all DNS lookups trough Avast DNS servers. Ironically this is basically DNS hijacking and breaks access to the Unblock All DNS servers. In order to get around this problem you have to disable the Secure DNS feature in Avast.
To enable or disable this feature, go to Settings (gear icon) → Active protection.
Next to Secure DNS, click on the ON/OFF switch.
If you are turning it off, you can choose whether to do so temporarily or permanently in the menu which appears.