2x Ukrainian Aircraft (Antonov 32) overflying Poland, they were flying with a switched off transponder until well into NATO airspace.
Currently at FL18, the aircraft have the callsign 32BLACK and 33BLACK. No idea where they are headed, might be Warsaw.
There's also the usual NATO01 Awacs, and JAKE11 RC-135 Rivet Joint SIGINT aircraft.
EDIT: 3rd Aircraft popped up on Radar, classign 04BLUE, yet another An-26. All these Aircraft are registered to the "Ukrainian Emergency Services"
EDIT 2: All aircraft en route landing at Bydgoszcz, Poland