"couchbase-server... is not commonly downloaded and could harm your computer"

When downloading Couchbase for Win64, I see a (pretty scary looking) warning message (see attached) which reads:

"couchbase-server... is not commonly downloaded and could harm your computer"

The default action presented is "Delete", with the only other choices being "Actions" and "View Downloads". Upon selecting "Actions" a dialog is presented (see attached 2) with "Don't run this program" as the recommended choice.

This gives a pretty bad first impression of the software, and may discourage people from actually clicking through to install it.

I believe (part of) the reason for this is a lack of signing for the Windows installer.