Microsoft, despite denials, appears to be in bed with the NSA. Apparently all encryption and other methods to keep documents and discussions private are bypassed and accessible by the NSA and whomever it is working with. This means a third party, for whatever reason, can easily access confidential business deals, love letters, government classified memos, merger paperwork, financial transactions, intra-corporate schemes, and everything in between.
With that said, do you really want to buy a Microsoft product? Do you want to buy anything that gives easy access to snoops poking around at their leisure? If you'd think twice about this, then why would a foreign government rely on Microsoft Office with any confidence? Personally, if I were any foreign government or corporation, I'd stop using all Microsoft products immediately for fear of America spying on me. Nothing can be secret.
If I was a shareholder in any public company, I'd get up at the annual meeting and ask if the company was using Microsoft products and if so, I'd demand to know why it has not dumped them for something else . . .