The answer to that question cannot possibly violate the privacy of any individual.
>> What’s more, McCullough argued, giving such a figure of how many Americans were spied on was “beyond the capacity” of the NSA’s in-house watchdog...
So, either: 1) They are totally disorganized ("dang, it's not like we keep a database we could SELECT COUNT(*) from, you know...") or 2) there is no way to estimate because they're doing wholesale collection of all the phone calls, web traffic, etc that they can get their hands on.
Pretty sure it's #2.