Dropbox for Business is good for collaborating on files stored in the cloud, but it hasn't had fine-grained permission control -- not great if you have a sensitive project you'd rather not share with the folks in Accounts Receivable. You'll be glad to hear, then, that Dropbox is introducing some much-needed access limits. You can now say which of your colleagues can edit or view a given file, and you can both set expiry dates and passwords for shared links. In other words, contractors won't get to peek at that big company report once their work is done. The new tricks are available through Dropbox for Business' early access program today, and there are promises of more features within a few months; they'll get the ability to search for text within files, work on Office documents with others and preview that same content on Android.