I've just experienced an odd problem on two new (late 2015) MacBook Pros both running Avast 11.7. Both join the home network and I suspect most other networks with no problem. However, the owner is taking lessons at a branch of the Stormfront Apple reseller here in the UK. The store has open access to its WiFi, but sends a landing page into which the user must log. Avast blocks the landing page - it just doesn't appear.
Turning WebShield off doesn't solve the problem and allow the landing page to appear. The only thing that works is to completely uninstall Avast, reboot the Mac and then the landing page appears immediately. Clearly, this isn't a satisfactory state of affairs.
Just to make thinks really odd, my old (late 2009) MacBook Pro, also running Avast and set up seemingly in the same way as the first two has absolutely no problem and sees the landing page.
Has anyone else experienced similar problems or can suggest a solution, otherwise I will have to find an alternative.