This is a common problem with many coins - it is being blocked because it contains mining software, and because some malware also contained such things to use people's computers for mining without their knowledge, anything with that in it gets labelled as a virus, even though it is not.

Older versions will still work, but they have the 'key compromised' message in them.  However that is just a message put there in error, it has no meaning.  Unfortunately once released the message cannot be recalled - which is why the latest version does not support any messages.

Current downloads and anything else are here: https://www.nyancoin.info/download.nyan