I started getting this alert today. I'm getting it on everything I try to do. Internet Explorer.
And I have not done anything in recent days to cause this alert. No Windows updates, no new programs, etc.
When this alert popped up as you see it in the image below I had placed a check mark in the box beside an e-mail in my mail box and was merely going to move it to another folder. That should not create a security alert.
Have you tried updating to the latest version of Internet Explorer via Windows Updates or Microsoft website to ensure you have up to date Security Certificate lists?
Give that a try..