If Avast really wants to get serious about limiting the usage of its Beta releases, which by the way I agree with @DavidR on this one they need to tighten up access to the Beta installer links.
This is what I would suggest.
1. Avast needs to start identifying the installer file as a Beta in the file name
2. Avast needs to start identifying the release as Beta in the GUI.
3. The forum needs to set up a Beta thread that users have to opt into in their profile in order to get to the Beta release download links. People who want to download the Beta should be required to opt into the Beta thread for each new Beta release.
4. Eliminate GUI updates for Betas.
5. Put up a big disclaimer and warning right above the installer links, not a one sentence comment about the release being a Beta release.