In the early to mid 2000s, the US rendered military aid to Georgia, in both training and equipment. This included unmanned aircraft.
In 2008, Russia invaded Georgia, and presumably captured some of those aircraft.
No security system should rely on the secrecy of its function, but in practice, many do. If any agency in the world can break the security of US UAVs, it'd be Russia.
Remind me again how the Russians and Iranians get along?