HAMDig uses SSL encryption, with a self-signed certificate. This may cause "Certificate not valid", "Authority Invalid", and/or "Your connection is not private" error messages in your web browser. This is simply the result of your computer not having the KC9UHI-CA Root SSL Certificate, which is used to validate the HAMDig website.
There are two ways to eliminate this message
First option is to download the certificate and install it using your computer's certificate manager. Searching the internet will provide directions for your specific operating system.
Section option (for windows computers) is to download the zip archive and run the included batch file, which will install the certificate for you. This is the contents of the batch file -- certutil -addstore -f -enterprise -user root "%~dp0kc9uhi-ca.crt"