Google has been encrypting search results for some time for users who are logged into their Google accounts.
What this means in English, is anyone who is logged into a google account, while doing a search, and then comes across your site and selects it, you will have no idea what key word they typed in to get to your page.
This has been freely available info for years, and has been a great way to analyse your site through analytics and work out what people type in to get to your site, or how your optimisation efforts are paying off for a particular keyword.
Google encrypted this results for logged in users in late 2011, and if you look in your analytics, when search for keywords, you might see the term "not provided"
Now Google has gone further and really pulled the rug from under us by encrypting all search queries, regardless of being logged in our not.
Search Engine Land has a good article on it, and they are speculating it is either due to recent controversy the NSA and spying allegations, or a way to force people to use adwords, which surprise surprise, you can see the keyword data
So on the one hand Google gives us great analytics functionality, and on the other starves us of the most important data
