If targetting iOS 4, you can use the Data Protection APIs.
If you have \'Full\' protection, does this encrypt the entire sandbox?
Specifically, If I download
My understanding is that you must use the data protection options. There was a WWDC 2010 talk on exactly this topic. See "Session 209 - Securing Application Data" which goes into detail. These videos are free and highly informative.
Login through developer.apple.com and then you can use the link in the page to get to the videos. FYI, the video contains all the example code you should need.
WWDC 2010 videos