All websites not secure using Safari
I can't get on the internet on another computer. I have Safari as my only web browser and every time I type in a URL I get a message that the site is not secure and do I want to proceed. I tried to install Webroot, but I was not able because it cautioned it couldn't get a secure web connection. I'm seeing my typed in URL change to something different than what I enter. When I look at Certificated, they are all out of CA, and not active, showing some future date. Just guessing, I'd say I've been hacked, but I don't know what to do next. Any advice appreciated.
MacBook Pro