When you don't know the affair partner's name or address

A lawsuit begins when the court sends the complaint (소장) to the defendant. So, as a rule, the complaint states the defendant's name and address. But few people know the affair partner's resident registration number or home address. Most come to a consultation knowing a name and phone number, or just a number.

You don't need to know everything from the start. Even one clue that distinguishes the person from others can be the starting point.

If you have several clues, write them all down. If one leads nowhere, you can search another way.

• Mobile phone number
• KakaoTalk ID or profile
• Bank account number left in transfer records
• Car plate number
• Workplace name and location
• Social media accounts

You file the lawsuit naming the defendant by the name you know or as "name unknown" (성명불상), and apply to the court for a fact inquiry (사실조회) to the mobile carrier. The court can ask public agencies or organizations to look into necessary matters (Civil Procedure Act (민사소송법) Article 294), and the carrier replies with the subscriber's name, address and other details. Once the reply arrives, the defendant's name and address are corrected and the complaint is sent again.

At this stage, you do not get to see the content of calls or messages. The procedure only confirms who uses the number. If it's a budget carrier (MVNO) line or a number registered in someone else's name, the reply may not identify the person, so we prepare other clues as well.

A reply to a fact inquiry can take several weeks. In the meantime the person sometimes changes their number, so it's good to keep a record of when you learned the number and of contacts made with it.

If there are records of your spouse sending money to the affair partner, a fact inquiry can be sent to that account's bank to confirm the account holder. Car plate numbers, messenger IDs and workplace information can also be used to identify the person. What can be asked of which institution depends on the clue, so we go through them one by one.

If you know their workplace, service can be attempted at their place of work even without a home address (Article 183(2) of the same Act). However, since the documents go to the company, keep in mind that the other person may react badly or the mood for a settlement may change.

Even with an address, service fails if no one is ever home or the person has moved. In that case, we reconfirm and correct the address or apply for service at night or on holidays. If that still fails, you can apply for service by publication (공시송달) (Article 194 of the same Act); the first service by publication takes effect 2 weeks after it is carried out (Article 196 of the same Act).

Because of this process, cases where you don't know the other person's details can take an extra few weeks to a few months before the trial really gets going. If little time remains on your time limit, it is safer to file with just the clues rather than waiting until you have all their details.

If the case proceeds by service by publication, the other person may receive a judgment without knowing a trial was held. As a result, finding their assets after the judgment can take time again.

Secretly finding out someone's address or contact details is prohibited by law, so if you hire an agency to do it, even you as the client can get into trouble. Secretly opening your spouse's phone or logging into their accounts to find information about the affair partner can also be punished.

Information obtained through court procedures must be used only for the lawsuit. Using that address to go to their home or to inform their family creates other disputes.

Looking up the affair partner's social media is not itself a problem, but approaching them with a fake account to dig for information or impersonating an acquaintance invites other disputes. Stop at saving public posts with the dates visible.

To apply for a fact inquiry, you must specify what the court should ask. Also prepare material showing where the clue came from. Rather than submitting just the number, the need for the inquiry becomes clear when there are records of that number being used to contact your spouse.

• For a phone number: call logs or message screens between it and your spouse
• For a bank account number: a transaction statement showing the transfers
• For a car plate number: a photo showing the plate and the date it was taken
• For a workplace: the company name mentioned in chats, or a photo of a business card