The latest version of Microsoft Office, Office 2013, has an entirely cloud-based life called Office 365, indicating that a subscription to it (and not a one-off payment for the software suite) is valid for one full year.
The good news for all students and university teachers is: Microsoft offers a subscription model for university use, aptly named Office 365 University, with a four-years-for-the-price-of-one subscription, one terabyte of online storage, and the benefit to be able to access and work on your Word document or Excel spreadsheet on a tablet on the go (as I do). I found it incredibly useful to have a software that I used for the last two decades in the cloud now.
More information on Office 365’s features can be found in this Business Insider blog by Julie Bort.