That isn't easy. Besides war, I see that lots of snipers did their work in between wars or during oppressions (currently snipers are busy in Syria). And from what distance is a shot defined as sniper shot? I have no clue but I am certainly interested in how this was measured, and of course: who was this "sneaky" person.
Any distance, as long as it's from sniper rifle. And you sir, are correct. Simo Häyhä A.K.A. White Death had around 500 confirmed kills with his rifle during Winter War (1939-1940).