According to Elcomsoft's researchers, Microsoft has done a great job beefing up the encryption of its Office documents. This has forced those who want to break it to move from brute forcing techniques to more advanced methods.
In a blog post the company says,
"Brute force becomes less and less efficient with every new release of Microsoft Office even with full-blown hardware acceleration in place. Office 2013 sets a new standard in document encryption, pretty much taking brute force out of the question. This is why we continue relying on a variety of smart attacks that include a combination of dictionary attacks, masks and advanced permutations."For now users of Elcomsoft's password
"Support for additional hardware accelerators such as ATI and NVIDIA video cards [is] scheduled for a later date."