anchor.diff:  
     src = fetchurl {
       url = "http://download.virtualbox.org/virtualbox/${version}/VirtualBox-${version}.tar.bz2";
  -    sha256 = "db84ddf47d1ecd316ec46417595f0252e3ec2f67e35e1e17320aba87b7c2934f";
  +    sha256 = "bc893adde4449a2d35d8b4d0b8b247f0f2ac62a434fd8a8f7c54f613a100855a";
     };
   
     buildInputs =
  
positive.code: 
  let
  
    version = "4.3.12"; # changes ./guest-additions as well
  
    forEachModule = action: ''
      for mod in \
  
negative.code:   '';
  
    # See https://github.com/NixOS/nixpkgs/issues/672 for details
    extpackRevision = "95030";
    extensionPack = requireFile rec {
      name = "Oracle_VM_VirtualBox_Extension_Pack-${version}-${extpackRevision}.vbox-extpack";
      # IMPORTANT: Hash must be base16 encoded because it's used as an input to
      # VBoxExtPackHelperApp!
      # Tip: see http://dlc.sun.com.edgesuite.net/virtualbox/4.3.10/SHA256SUMS
      sha256 = "b965c3565e7933bc61019d2992f4da084944cfd9e809fbeaff330f4743d47537";
      message = ''
        In order to use the extension pack, you need to comply with the VirtualBox Personal Use
        and Evaluation License (PUEL) by downloading the related binaries from:
  