There are 2 things I want to address.
First off, an auto-download does not mean auto-run, does it? Why would downloading the thing be an issue in the first place as long as you don't manually execute it, as that is what every single virus does and activates.
Secondly, would this even be an issue for browsers that don't even have auto-downloading and asks you where to download it before (with even Chrome having such an option anyway)?