IMPORTANT: If you have run Install Updates from the 25th onwards, then you are no longer vulnerable.
You bash version should now be > 4.3-7ubuntu1.3
To find out if you have the above version or higher, open a terminal and do (in 32 and 64 bit):
dpkg -s bash | grep Version
Run the 2 commands below from the terminal one at a time, each time it should return the word safe. If it returns the word vulnerable then do Menu, Install Updates and test again.
env X="() { :;} ; echo vulnerable" /bin/sh -c "echo safe"
env X="() { :;} ; echo vulnerable" bash -c "echo safe"
Alternatively you can do:
sudo apt-get update && sudo apt-get install bash
to get the latest version of bash.