False positives are an issue and point of concern for all forms of IT security monitoring and no one is exempt from making a mistake.  When the mistake defames a large organization like Dropbox, eyebrows are raises and concerns voiced.  Krebs does a good job walking through this particular instance in his blog post.

http://krebsonsecurity.com/2016/06/dropbox-smeared-in-week-of-megabreaches/