Yes, lurk is a Scrabble word!
...and is worth 8 points in Scrabble, and 10 points in Words with Friends
lurk
Verb
1. Lie in wait, lie in ambush, behave in a sneaky and secretive manner
2. Be about
3. Wait in hiding to attack
Verb
1. Lie in wait, lie in ambush, behave in a sneaky and secretive manner
2. Be about
3. Wait in hiding to attack