Out of the network, into the cloud
Speaking of BYOD blacklisted apps, some of the most hated ones - at least by CIOs - are cloud storage service offerings such as Dropbox. Confidential corporate data can find its way into these consumer repositories and out of the reach and purview of IT.
An employee can whip out his BYOD smartphone, take a picture of a whiteboard or a screen shot of an important document and save the image in Dropbox, and there's nothing IT can do about it. If your company supports BYOD, you can bet there's corporate data in a consumer cloud service.