I would argue that from an engineering standpoint, Dropbox is more secure having been attacked in the past - they've had a review of their company policies, and

I would argue that from an engineering standpoint, Dropbox is more secure having been attacked in the past - they've had a review of their company policies, and worked on preventing issues that might crop up in the future. That being said, an option to disable preview icons doesn't seem like a worthy use of time. After all, if you're signed into your Dropbox account on a PC, you probably have all of the data on that PC from Dropbox. If selective sync is on, an attacker could easily add folders as well. Security by obscurity isn't security.