```ruby
class Virtualbox < Cask
  url 'http://download.virtualbox.org/virtualbox/4.2.10/VirtualBox-4.2.10-84104-OSX.dmg'
  homepage 'http://www.virtualbox.org'
  version '4.2.10-84104'
  sha1 'e4d016587426c1ef041bd460905b5385e566fe77'
end
```

Upgrade Virtual box to 4.2.12
user
```ruby
class Virtualbox < Cask
  url 'http://download.virtualbox.org/virtualbox/4.2.12/VirtualBox-4.2.12-84980-OSX.dmg'
  homepage 'http://www.virtualbox.org'
  version '4.2.12-84980'
  sha1 '9a5913f0b25c69a67b554caa9bebd1a4d72d3d00'
end
```
assistant