The experiment involved a group of college students that played for five minutes as one of three avatars in a game: Superman (hero), Voldemort (villain), or a circle (neutral). After the gaming session, participants then had to decide how much chocolate sauce or chili sauce to give to other participants in a supposedly unrelated taste test. As it turns out, those who used the Superman avatar poured twice as much chocolate sauce (symbolizing a "good" deed) than chili sauce (a "bad" deed), whereas those who played as Voldemort did exactly the opposite. The study authors suggest a possible explanation for these effects might be related to the lasting influence of total immersion in a virtual environment.
[Thanks to Jose for the tip!]