Invalid certificate message. Redirect or dns issue?

Hi there, sorry if this is the wrong subforum, please move if so!

I am trying to diagnose an internet browsing issue on a ~March 2012 Imac running 10.7.4.

I believe it to be a redirect or possibly a hijacked dns.

Connected via ethernet, wireless disabled, network diagnostic tools returns no errors. Have run ClamXAV for what it's worth, nothing came back. Checked for Flashback, clean there too.

When attempting to ping facebook.com, amazon.com, tumblr and a few others one gets the following:

Invalid URL

The requested URL "/", is invalid.
Reference #9.f2c38f18.1346385136.229cc0ea

or

http://i846.photobucket.com/albums/ab29/pdarkfred/error.png

Looks about the same in any browser, seems to load only bits of the page. Crops up at random, but about 40% of the time it's not working correctly.

Any help would be very welcome!

Thanks,
Aki

I've had that happen on occasion. I've noticed that clearing my cache/cookies, etc works to fix that those issues. I don't know about the pinging thing but definitely with the image you attached.