According to Apple's update notes, iOS 6.0.1 update fixes some security vulnerabilities found on iOS 6. One such issue has to do with Passbook and how a person could access it without entering a passcode.
As described by Apple:
Available for: iPhone 3GS and later, iPod touch (4th generation) and later, iPad 2 and later
Impact: A person with physical access to the device may be able to access Passbook passes without entering a passcode
Description: A state management issue existed in the handling of Passbook passes at the lock screen. This issue was addressed through improved handling of Passbook passes.