Artemis Seaford, a dual U.S.-Greek national, was targeted with a cyberespionage tool while also under a wiretap by the Greek spy agency in a case that shows the spread of illicit snooping in Europe.

U.S. officials now suspect that the balloon was sent to spy on bases in Guam and Hawaii and that other downed objects were not surveillance machines. Washington’s evolving view reflects U.S. and Chinese difficulties in discerning each other’s intentions.