Maxwell's demon objection
Maxwell's demon is a thought experiment that shows how the Second Law can be violated. Take a container divided into two parts containing gas, and imagine that the 'demon' controls a gate between the two only allowing 'hot' molecules to go into one compartment, leading to increased entropy.
Responding to this thought experiment has prompted a revised characterization of the Second Law that explicitly takes account of information - indeed some have argued that the Second Law needs to be re-characterized in terms of information dynamics, rather than energy dynamics (elaborated in this node's subtree).