Yet another inverted idea from Terry Pratchett's Discworld (like knurd and Bloody Stupid Johnson). In this case it's blackmail inverted, although it might still be considered extortion. Imagine you're a mafioso. Now, you want the tough guy image, right? So, if it is disclosed that you are donating 100 dollars every week to an orphanage ... it'll damage your reputation. Hence, if someone threatened to disclose your good deeds, unless you paid them an exhorbitant amount of money, this would be whitemail.