You have experienced one of Microsoft's first bad updates in quite some time! KB2589275 was an Office update rollup that happened to break the file associations with Word and Excel documents, and a handful of others. The Microsoft team has provided the problem, and the fix, very nicely in a blog post of their own, which you may read at:
Our CommonFocus customers are already benefiting from our patch management service, in that we have turned off deployment for this patch and rolled it back from the small number of machines which were already affected. And if you are not currently a CommonFocus customer, but are interested in exploring becoming one, feel free to contact our very own Nick Stevenson at nstevenson@pointsolve.com for a quote.