Jailbreaking allows applications not approved by Apple to be downloaded from any source, and it removes the securitycontrols which prevent access to data on the device by unauthorized people and applications.
In addition, by embedding security and privacy controls into structured data and metadata, data owners can focus more effort on ensuring the safe and secure delivery of data to the end customer and fewer resources on securing the device that will receive the data.
No matter what they say, how much they protest that privacy controls are in place, or how senior their security executive is, your data is visible to someone.