You have a serious problem. The valid site is signed with a valid Entrust certificate. https://www.ssllabs.com/ssltest/analyze.html?d=isapps.acxiom...
Are you at work or on a coffee shop network where SSL traffic might be intercepted?
Are you at work or on a coffee shop network where SSL traffic might be intercepted?
This intermediate certificate must instead be downloaded by the browser. I suspect, therefore, that some browsers do not have the intermediate certificate and so the certificate cannot be validated.
[0] https://www.ssllabs.com/ssltest/analyze.html?d=isapps.acxiom...
I work for a security company so have zero expectations of privacy when I'm on the corporate network (which I was here) but I also see the same issue on both 3 and EE in the UK.
I don't generally see issues like this on the corporate network so there's something different about this case.
Of course Acxiom really should serve the site and intermediate certificates together to reduce round-trips and speed up the handshake.