A lot of AV engines use crowdsourced classifiers like virustotal to flag “potentially unwanted applications (PUA)” as a threat and quarantine, but the term “malware” is a category reserved for destructive or criminal application behavior. I’m not convinced that is what was or is bundled with “sponsored” Filezilla installers.
At some point the bundled adware was apparently something called OpenCandy related to ask.com, and the developer of FileZilla is alleged to have concealed rather than disclosed it.[2]
The adware-free installer was/is reported to be available for download freely on the same site, but for the extra browsing effort.
[1] https://web.archive.org/web/20190526065704/https://forum.fil...
[2] https://malwaretips.com/threads/sourceforge-net-adds-adware-...