The Patent and Trademark office doesn’t do much research looking for prior art before issuing patents. Several years ago they gave Roger Billings a patent on networking. IBM and Xerox had been networking for years before that but PTO ignored that little fact. The courts finally invalidated the patent. Google is likely talking about such patents, and they can probably show prior art when required.
I think what they are going to find is that the "prior art" had been created and patented by Novell & Nortel and was known to have been patented when Google started using it and that MSFT et al legally acquired the rights to it.
In fact, it appears MSFT asked Google to join them in making the purchase