Doubt it's been hacked but a possibility. I think either it's a safety measure programmed by the boffins at google in an attempt to warn people of dangers.
I search say 'jim biob' the problem is there, then click search it AGAIN and it goes, and the search again and it appears, then search again and it goes!!!! f*&kl this I'm of too yahoo!
Now I get a site with: Your client does not have permission to get URL /interstitial?url=http://www.google.de/ from this server. (Client IP address: xxx)