Scurrilously is how you do something when your words are scurrilous: you speak or write in a low, damaging way, often with untrue or unproven claims meant to hurt someone. Same formal, written feel as scurrilous. You will almost only meet it in news, law, or books. In everyday talk, people just say someone “spread nasty lies” or “tried to smear her.” The -ly does not make the attack milder; it only turns the adjective into a way of speaking or writing.