Trick that Will Keep You To Protect From Government Spies

Last week, the German government arrested someone and charged him with spying for the US. Buried in one of the stories was a little bit of tradecraft. The US gave him an encryption program embedded in a -- presumably common -- weather app. When you select the weather for New York, it automatically opens a crypto program. I assume this is a custom modification for the agent, and probably other agents as well. No idea how well this program was hidden. Was the modified weather app the same size as the original? Would it pass an integrity checker?
Related: there is an undocumented encryption feature in my own Password Safe program. From the command line, type: pwsafe -e filename