Germain Grisez and the Catechism on Detraction

Detraction, or wrongfully harming another person's reputation by disclosing their faults without good reason, is in itself a grave sin, according to the moral theologian Germain Grisez (The Way of the Lord Jesus, vol. 2, ch. 7, question B, section 5.g ff.; http://twotlj.org/G-2-7-B.html). Reparation must be made. Also, not everyone has the unconditional right to the truth. From the Catechism of the Catholic Church:

2477 Respect for the reputation of persons forbids every attitude and word likely to cause them unjust injury. He becomes guilty: 

• of rash judgment who, even tacitly, assumes as true, without sufficient foundation, the moral fault of a neighbor; 
• of detraction who, without objectively valid reason, discloses another's faults and failings to persons who did not know them; 
• of calumny who, by remarks contrary to the truth, harms the reputation of others and gives occasion for false judgments concerning them. 

2478 To avoid rash judgment, everyone should be careful to interpret insofar as possible his neighbor's thoughts, words, and deeds in a favorable way: 

Every good Christian ought to be more ready to give a favorable interpretation to another's statement than to condemn it. But if he cannot do so, let him ask how the other understands it. And if the latter understands it badly, let the former correct him with love. If that does not suffice, let the Christian try all suitable ways to bring the other to a correct interpretation so that he may be saved. [St. Ignatius of Loyola, Spiritual Exercises, 22.]

2479 Detraction and calumny destroy the reputation and honor of one's neighbor. Honor is the social witness given to human dignity, and everyone enjoys a natural right to the honor of his name and reputation and to respect. Thus, detraction and calumny offend against the virtues of justice and charity. [...] 

2487 Every offense committed against justice and truth entails the duty of reparation, even if its author has been forgiven. When it is impossible publicly to make reparation for a wrong, it must be made secretly. If someone who has suffered harm cannot be directly compensated, he must be given moral satisfaction in the name of charity. This duty of reparation also concerns offenses against another's reputation. This reparation, moral and sometimes material, must be evaluated in terms of the extent of the damage inflicted. It obliges in conscience. 

2488 The right to the communication of the truth is not unconditional. Everyone must conform his life to the Gospel precept of fraternal love. This requires us in concrete situations to judge whether or not it is appropriate to reveal the truth to someone who asks for it. 

2489 Charity and respect for the truth should dictate the response to every request for information or communication. The good and safety of others, respect for privacy, and the common good are sufficient reasons for being silent about what ought not be known or for making use of a discreet language. The duty to avoid scandal often commands strict discretion. No one is bound to reveal the truth to someone who does not have the right to know it.