Feralheart is malware free and doesn't contain any maliciou software in it's setup/download. Even though FH itself is safe, we cannot promise all player made mods are.
Some antivirues and Google Chrome dislike FH because it's an uncommon download.
There should be an option to add a site you your antiviruses "safe list/exceptions list." Just look for that, add "Www.feral-heart.com" to it, and try downloading the setup once more.
Also try lowering your browser's security and firewall temporally.
Also, this belongs in game help. :3