I am having the same issue as Jame_s was originally, so when I try the sudo get-apt update I get the hash sum mismatch error. When I try sudo apt-get upgrade I get:
pi@raspberrypi ~ $ sudo apt-get upgrade
Reading package lists... Error!
E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/mirrordirector.raspbian.org_raspbian_dists_wheezy_contrib_i18n_Translation-en
E: The package lists or status file could not be parsed or opened.
pi@raspberrypi ~ $
It is a strange issue, and I have tried many times on Friday and today so I don't think I am catching them at some kind of server update unless I have the worst luck in the world.