lurk: (lûrk) 1. to lie in wait, as in ambush. 2. to move furtively; sneak. 3. to exist unobserved or unsuspected.
stalk: (stôk) 1. to pursue by tracking stealthily. 2. to follow or observe (a person) persistently, especially out of obsession or derangement. 3. to go through (an area) in pursuit of prey or quarry.
so you see, there is a difference.