NATO troops' smartphones are under attack by Russian hackers bent on obtaining information on and exploiting soldiers as well as getting a handle on NATO military capabilities.

The hackers have so far accessed the phones of 4,000 NATO troops in Europe, the Wall Street Journal reported, using the phones in conjunction with surveillance drones to eavesdrop on troops in the Baltic states and Poland who are guarding the Europe-Russia border.

The report cited U.S. Army Lt. Col. Christopher L'Heureux as among the troops hacked. L'Heureux said that when he recently returned to his truck after participating in shooting drills, he found his phone hacked and reported lost.

“They were geolocating me, whoever it was,” the Journal quoted the officer, who plots troop positions to defend against a Russian attack, as saying. “I was like, ‘What the heck is this?'”