There tends to be a lot of myths about Microsoft security particularly in the non-Windows using community. The fact of the matter is that Microsoft tends to be very good about security updates, disclosure of bugs and holes, and remains vigilant about finding and patching up unknown flaws. Additionally, Microsoft hasn't had to answer before Congress on the matter of the securing their user's data. So trying to compare Microsoft's apparently "embarassing security failures" to Dropbox having to testify to Congress is like comparing your post to a PG essay.