That's exactly what it is. The same thing happened to me I kept getting the message from IBO. At first, everything was fine then I switched browsers and started getting the message. After doing research I found it was because I hadn't changed from http to https. Once I did the warning message went away.
Your website need a SSL Certificate (also referred to as a “digital certificate”) ...
SSL Certificates provide secure, encrypted communications between a website and an internet browser.