I have never seen this kind of behavior before.
This morning I start to get this message on all the computers when try to access internet using internet explore. If I use Google Chrome, The internet works fine. Same machine>>Internet explorer works fine if I switch to a different internet connection.
The network where Internet Explorer stop working, I have a firewall/DNS/proxy. I removed the proxy by assigning the IP manually and open all the port on firewall but this doesn't let Internet Explorer working and same machine Google Chrome is working fine.
I am not sure what and where to look at this point. I have update/scan all the virus already.
Let me know if you need any more info to suggest or recommend something.