A country cannot be on the United States' good side without bending to its will. Also, the governments of other countries would love to have a peek on whatever intel the NSA has regarding their enemies.
So, if the US wants your data, they have great diplomatic resources to compel a country to hand it (read: CIA). I'm speculating as I don't know if there is a precedent of the US requesting data from another country using secret warrants, but as long as they have a warrant and the country does not have an overtly adversarial relationship with the US, it's a target.
Based on their tradition of bank secrecy, Switzerland may be an exception, but I wouldn't bet on it.
The US doesn't need a 'secret warrant' to ask for information from another country. They don't really need a warrant at all. They just ask for it. IIRC, even the NSA isn't legally bound to avoid spying on American citizens when they are out of the country.
To avoid it, no. But if they do uncover evidence on American citizens it could not be used in a trial and must be filtered out (although, see 'parallel construction').
So, if the US wants your data, they have great diplomatic resources to compel a country to hand it (read: CIA). I'm speculating as I don't know if there is a precedent of the US requesting data from another country using secret warrants, but as long as they have a warrant and the country does not have an overtly adversarial relationship with the US, it's a target.
Based on their tradition of bank secrecy, Switzerland may be an exception, but I wouldn't bet on it.