Just an update
I have since downloaded from this link and Avast did not complain.
so I am assuming that this particular downloadable file is free from malware/pup/virus etc.
https://filezilla-project.org/download.php?show_all=1I selected for x64 bit windows
FileZilla_3.13.1_win64.zip
I noticed that when I attempted to do the same process again (to supply a link to this post) from the renewed link page that the file name was different, giving me the impression that there was a later version based on its file name!
I backed tracked and the link I have supplied is exactly the steps I took.
File details are
version 3.13.1.0
filezilla.exe Monday, 24 August 2015, 3:56:48 PM actual size 11.5 MB (12,098,520 bytes)
all the other files appear to be date stamped exactly the same as above.
certificate details
Hope that helps others who may have had this problem.