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.”

Links:
https://www.aldrimer.no/claims-russian-special-forces-are-operating-inside-estonia/
http://news.postimees.ee/3680481/experts-say-lion-s-share-of-nato-leak-is-hot-air
http://tehnika.postimees.ee/3682041/drooniluureskandaal-eestlaste-koned-on-rangelt-kapo-kontrolli-all