Tried to install the Avast Security pkg on the latest public beta of macOS Catalina and was give a popup saying the installer can’t be opened because it can’t be checked for malicious software. this software needs to be updated.
I’ve got the same issue as well. Currently on 10.15 build number 19A512f (Public Beta 3)
Tom,
I hope the Avast Mac development group is on top of this and it would be nice if someone from Avast would reply to this post.
Steve
I completely agree - in the mean time though have just found that if you right click on the installer and select ‘Open’ it will allow you to install it 
Not a solution but a workaround whilst on the Beta
Thanks for the tip!
Steven204 - as the version 14.0 was released - would you mind to retest with it? It should work.