Section — Wouters, Manual of Moral Theology
§ I. On the Office of Preserving the Sacramental Seal
The law of the sacramental seal1 can be taken in a broad and in a stricter sense. Taken in a broad sense, it is the law which forbids the use of sacramental knowledge which is of a nature to redound to the burden of the penitent, and therefore, if it were licit, would render confession more difficult. I said "which is of a nature," etc., because it does not matter whether the penitent notices the use or not; it suffices that in itself it involves a burden.
Taken in the stricter sense, it is the law which forbids the use of sacramental knowledge together with manifestation, or danger of manifesting the penitent.
The prohibited use of sacramental knowledge, or violation of the sacramental seal, is distinguished as twofold: direct and indirect (cf. can. 2369, § 2). Direct violation is the use of knowledge acquired from confession together with manifestation of the sinner. Wherefore observe that it is not required that the person of the penitent be known, but it suffices that the person be sufficiently determined; for instance, if I say concerning a person meeting me and unknown to you that he or she confessed this or that. Indirect violation is judged to be the use of knowledge acquired from confession which has annexed to it the danger that the sinner be betrayed, or which involves a burden of the penitent with or without danger of manifestation of the sinner.
These things having been noted, we shall speak first of the obligation, then of the object, then of the subject of the sacramental seal, and finally we shall deduce certain corollaries from the things set forth.
1 So called because that law covers the things heard in confession as with a seal.