According to court documents and interviews with people associated with the program, FBI used spywares sent to computers and phones either through links or emails.
It is the same technique used by cyber criminal nowadays.
One hacking tool developed by the FBI can remotely activate microphones running Android OS to record conversation without user knowledge. It can also do the same thing to laptops.
It comes shortly after news reveals US helped New Zealand spy on Journalist Jon Stephenson.
For more revelations about the FBI, head over to WSJ.