Users who have installed Avast Mac Security with Web Shield have reported that they're unable to connect to several of OU's websites, including learn.ou.edu and ozone.ou.edu. When someone tries to navigate to one of the blocked sites, their browser displays an error message saying that the connection couldn't be established. This error seems to be limited to OU websites that use HTTPS, or secure HTTP, to connect.
A workaround for this issue is to disable Web Shield within Avast's settings. To do this, open Avast, click on 'Preferences,' and then on 'Disable' within the 'Web Shield' settings. Another workaround would be to uninstall Avast altogether. Using the installer that was used to install Avast, click on 'Uninstall Avast' in the popup window and follow the prompts to completely remove Avast from your system. Either of the previous options should restore access to the blocked OU websites.