It's not just tech industry giants contributing, either. Supporters range from oil giant BP through to the Electronic Frontier Foundation and Fox News. Even five former Department of Justice and FBI officials are supporting Microsoft.

There's no guarantee this will work. The Justice Department insists that Microsoft has no grounds for its lawsuit, that there are steps to protect rights and that there's a "compelling" interest in keeping criminal investigations secretive. However, as with tech companies supporting Apple in its battle against the FBI, the brief is a reminder that any ruling will have an effect on the rights of many people, not just Microsoft's users.