Musar על ערכין 31:5

In these parashiyoth, the Torah wrote at length about the greatness of the uncleanliness of the metzora [one afflicted with tzara'ath (leprosy)] and of his cleansing. And the Gemara in Arachin is well known, that tzara'ath afflicts one who speaks lashon hara, as stated there (Arachin 15b): "If one speaks lashon hara, he is afflicted with plague-spots, viz. (Psalms 101:5): 'He who slanders his neighbor in secret, him atzmith,' and (Vayikra 25:30): 'latzmituth,' which the Targum renders 'lachalutin'; [that is, that he be a metzora muchlat], concerning which we learned: 'The only difference between a quarantined leper and a confirmed [muchlat (similar to 'lachalutin')] leper is disheveling of the hair and rending of the clothes" [(these obtaining with the second, but not with the first)]. As to (Arachin 16a): "Plague-spots come for seven things, etc.", the Maharsha writes that there, it is possible that tzara'ath atones for him, for he is subject to quarantine — as opposed to the sin of lashon hara, where he is a metzora muchlat.

Then there is he who speaks gossip by way of deceit: he tells it with seeming innocence, as though he does not know that he is indulging in gossip, and when others rebuke him he says, "I really don't know whether so and so is guilty of these things." Or he says, "This may be merely gossip." One who speaks words that cause harm to his fellow man, whether it be to his body or to his money, even though it be to distress him or to frighten him, it is gossip. If a man says something to his companion, he is forbidden to reveal it without his permission (Yoma 4b). But anything which a man says in front of three people it is as though he intended it to be common knowledge and if one of the three who heard it told about it we cannot say that this is gossip (Arakin 15b). But if the teller intends to reveal more than he heard, then there is something of gossip in it. And if the speaker warns those who heard him not to reveal it, even though he speaks in the presence of many people, still if one of those who were warned does reveal it, it is a sort of gossip. There is a story about a certain pupil who revealed a thing that had been said in the house of study twenty-two years earlier and they drove him out of the house of study and they said, "This one is a revealer of secrets" (Sanh. 31a).