Ridiculous,seems like they are taking data and storing it and waiting to get subpoenas to look into and analyze the data later. Welcome to the new world order where your every movement is known.
These caches of information exist all over the place. While I'd prefer NDA/GCHQ to not slurp and store this stuff at least they have a duty to keep it secret. I am a lot more bothered by my ISP keeping that stuff. They're a lot less competant and have many fewer access controls.