Sounds like your DNS requests are being intercepted at the network level. Probably an infected router, but it could also be an evil ISP.
If it happens even when you're on (for example) public wifi, then it's malware on your own computer.
If it happens even when you're on (for example) public wifi, then it's malware on your own computer.
It's funny because sometimes if I go to facebook.com, it pops up with an SSL error - saying the site certificate belongs to another domain (eg: nonfacebook.com). Usually a reboot fixes it.
It could even be something that infected your router, such things exist. http://it.slashdot.org/story/09/03/23/2257252/botnet-worm-ta...
You shouldn't take this lightly, and definitely shouldn't bank online or otherwise do anything that should require any kind of security until you resolve this.