Hello, this is Attorney Eom Sang-yoon of Cheongchul Law Firm.

In civil disputes such as claims for damages arising from a spouse's infidelity or claims against employees for misconduct, parties often need to obtain evidence that falls within the other side's private domain. In this process, parties may secretly record conversations of the other party or third parties, or photograph text messages and pictures stored on the other party's mobile phone.

The problem is that even when such evidence clearly reveals the substantive truth of the dispute, the very process of collection may violate the Protection of Communications Secrets Act (통신비밀보호법) or the Act on Promotion of Information and Communications Network Utilization and Information Protection (정보통신망법, hereinafter the “Network Act”).

Today, we will examine the admissibility of illegally obtained evidence in civil litigation through Korean Supreme Court Decision 2024Da222212 (April 30, 2026).

[Relevant Statutory Provisions]

The Protection of Communications Secrets Act provides that no person may record a conversation between others that is not open to the public (Article 14, Paragraph 1), and that recordings made in violation of this prohibition are subject to the evidentiary-use ban under Article 4 (Article 14, Paragraph 2). In other words, where a third party secretly records a non-public conversation between others, the resulting recording file or transcript is expressly prohibited from being used as evidence in any trial or disciplinary proceeding (see Supreme Court Decision 2020Do1538 of January 11, 2024; Supreme Court Decision 2023Meu16593 of April 16, 2024).

On the other hand, the Network Act prohibits damaging another person's information processed, stored, or transmitted via an information and communications network, or infringing, misappropriating, or disclosing another person's secrets (Article 49), but contains no separate provision regarding the admissibility of evidence collected through such violations.

Meanwhile, the Civil Procedure Act adopts the principle of free evaluation of evidence (Article 202) but, unlike the Criminal Procedure Act, contains no provision excluding the admissibility of illegally obtained evidence. As a result, except where individual statutes such as the Protection of Communications Secrets Act expressly address admissibility, there is no unified standard for determining the admissibility of illegally obtained evidence in civil litigation.

[Holding in Supreme Court Decision 2024Da222212]

The case involved a plaintiff who alleged that the defendants had engaged in an affair with the plaintiff's spouse A and sought damages against them. The plaintiff submitted two types of evidence as follows.

1. Recording evidence: Recording files and transcripts of conversations between A and some of the defendants, obtained by secretly installing a recording device in A's vehicle (in violation of Article 14, Paragraph 1 of the Protection of Communications Secrets Act).

2. Mobile phone evidence: Photographs taken by the plaintiff with his own mobile phone of text messages, pictures, and videos stored on A's mobile phone (in violation of Article 49 of the Network Act).

The Supreme Court reached different conclusions regarding the admissibility of these two types of evidence.

1. As to the recording evidence, the Court held that because the recordings constituted files or transcripts of conversations between others that were not open to the public and were obtained in violation of Article 14, Paragraph 1 of the Protection of Communications Secrets Act, their admissibility was denied under Article 14, Paragraph 2 and Article 4 of the same Act. The Court made clear that where an individual statute expressly excludes admissibility, that exclusion cannot be avoided even in civil litigation.

2. As to the mobile phone evidence, although it was collected through conduct that violated Article 49 of the Network Act, the Court held that since neither that Act nor any other individual statute contains a provision on admissibility, its admissibility is not uniformly denied. The Court further held that admissibility in such cases must be determined individually by balancing the protected interest of the other party's personal interests and the like against the value of discovering substantive truth, on the basis of the fundamental principles of civil procedure—fairness of trial and good faith.

The Supreme Court further identified the following factors to be considered in this balancing test: (i) the nature and content of the case; (ii) the actor, circumstances, and method of the unlawful conduct in question; (iii) the nature of the infringed interest and the content and degree of the harm; (iv) the relationship between the parties involved in the unlawful conduct and the pattern of the dispute; (v) the characteristics of the matter to be proved by the unlawfully obtained evidence; and (vi) the necessity and urgency of obtaining the evidence.

Applying these criteria, the Supreme Court took into account, among other things, the facts that (i) evidence concerning infidelity inevitably relates to an individual's private life by its very nature, (ii) at the time the evidence was collected, the plaintiff and A were legally married and maintained a cohabiting relationship, (iii) the photographing of the evidence took place within the residence in which they cohabited, (iv) the privacy and personal interests of A and the defendants could not be deemed to have been gravely infringed, and (v) the necessity and urgency of securing the evidence were recognized. On these grounds, the Court affirmed the admissibility of the mobile phone evidence, upheld the lower court's finding of infidelity, and dismissed the appeal.

[Practical Implications]

In light of the rules established by this decision, the following points warrant attention when collecting evidence to prove infidelity, detect employee misconduct, or establish leaks of corporate confidential information.

• Secretly recording “conversations between others that are not open to the public” may not be effective in terms of evidence gathering. Such conduct directly violates Article 14, Paragraph 1 of the Protection of Communications Secrets Act and may be subject to criminal punishment; moreover, Article 14, Paragraph 2 and Article 4 of the same Act expressly deny admissibility in civil litigation as well, so the recording cannot ultimately be used as evidence. However, where one party to the conversation himself or herself does the recording, the conversation does not qualify as a “conversation between others,” and the above provisions do not apply.

• Where illegally obtained evidence is not subject to any express statutory exclusion (such as evidence collected in violation of the Network Act), it is essential to recognize that, although admissibility may be recognized, the outcome of the balancing test can vary depending on the circumstances of each case. The decisive factors that led the Supreme Court to recognize admissibility in this case were (i) the unique character of the matter to be proved, namely infidelity; (ii) the parties' relationship as a legally married couple living together; and (iii) the special location of collection, namely within their shared residence. The outcome may well differ where (i) the couple is separated or already divorced, (ii) the dispute is between third parties outside any family relationship, or (iii) the collection involved unauthorized intrusion into a space outside the residence.

• Furthermore, where the process of collecting evidence may itself constitute violations of the Network Act, the crime of trespassing on residence, the crime of infringement of secrets, and the like, there is a risk of criminal punishment in itself. The legality of the collection method must therefore be carefully reviewed before securing the evidence. Even if the evidence is admitted in civil litigation, separate criminal liability may not be avoided.

Where one must attempt to prove a case through illegally obtained evidence, it is necessary to thoroughly organize materials regarding the circumstances and necessity of the evidence collection, so as to be able to assert and demonstrate, beyond mere admissibility, the factors considered in the balancing test, such as (i) the necessity and urgency of obtaining the evidence, (ii) the minimal nature of the infringement, and (iii) the reasonableness of the collection method. Submitting materials that support the legitimacy of the collection, rather than merely submitting the evidence itself, will be the more effective way to enhance the prospect of admissibility.