The NSA's link analysis identifies persons communicating with foreign entities and targets them for further investigation. In fact, in the world of security clearances, doing business with foreign entities can get you classified as a "non US Person" whether you are a US citizen or not.
So, how many of you have received the ubiquitous letter from that wealthy Nigerian ex-government minister wishing to transfer funds overseas? Communicating with foreign national? Check. Possible involvement in transfer of funds from/to overseas? Check.
You're on the list, buddy!
It wouldn't surprise me at all if a certain number of these 419 scams were NSA pretexts to justify further surveillance.