Verbs

(v)lurk, skulklie in wait, lie in ambush, behave in a sneaky and secretive manner
(v)loiter, lounge, footle, lollygag, loaf, lallygag, hang around, mess about, tarry, linger, lurk, mill about, mill aroundbe about a place without any apparent purpose“The high school students like to loiter in the Central Square”, “Who is this man that is hanging around the department?”
(v)lurkto monitor a web forum or similar without making your presence public