on wyBuild features page it is written that. "it even supports downloading from sites using self-signed SSL certificates. "
We provide this as a convenience to customers who work on intranets that are misconfigured (which is a *lot* of them).
For example in chrome if certificated is not signed it warns the user. If the certificate is not signed wyUpdate should not update in my case.
It sounds like you want to use update signing. If the updates are altered with then they won't be installed.
Tell me if that helps.