When I was in Yeshiva, someone somewhere in Klal Yisrael played a practical joke. Sometime during the week of Parshas Vayeishev, a text message went around saying something to the effect of "a 17 year old boy was kidnapped by Arabs. Please daven for Yosef ben Rachel." Someone in my Yeshiva received the text message, and showed it to the Gabbai at the end of seder, who proceeded to go to the bima and lead recitation of Tehillim on behalf of this boy. The "joke" was that no one was kidnapped, and Parshas Vayeishev is when Yosef (ben Rachel) was sold through Yishmaelim down to Mitzrayim.
The inappropriateness of it notwithstanding, does this jokester get schar (reward) for having been the catalyst of the sincere recitation of many people? All of those reciting Tehillim were doing it sincerely, and they were reciting verses (so it doesn't seem to be tefillas shav). Does he get credit for having caused something positive?
We find in midrashim that there is a concept of reward even for positive acts done with negative intentions, for example Moshe was afraid to confront Og because he had the merit of having informed Avraham that Lot was kidnapped, and this despite the midrash which says that Og's intention was that Avraham should be killed in battle.