In April 2015 NATO brought their special forces to Estonia for a secret NATO exercise. In the days that followed Russia unleashed a series of aggressive counter measures to monitor their exercises.
Estonian signals intelligence quickly discovered an IMSI-catcher – a false cell phone tower in the local cellular network. NATO believes that the Russians attempted to identify the key NATO personnel.
Classified NATO report: “The ghost tower came online briefly twice during the day. It overtook all local towers and hijacked all the local recipients before it dropped offline.”