You have a man in the middle listening to your traffic. It may be an unwanted proxy server. This is exactly why there are HTTPS sites, to warn you against this.
To check for a proxy, hit Windowskey-R (Run) and type control inetcpl.cpl,,4 (exactly like that) then hit enter.
In the Internet Properties window that pops up, click "LAN settings". In the popup, make sure all three checkboxes are cleared, especially the one for "Proxy server".
Hope this helps.
