The legal risk surrounding the leakage of corporate secrets has dramatically escalated due to the revision of the Unfair Competition Prevention Act (UCPA), effective July 2024, and critical precedents from 2025. The notion that an employee’s “post-resignation duty of confidentiality” simply “expires after a few years” is no longer valid.
Latest case law, such as a ruling ordering approximately ¥210 million JPY in damages for the use of a customer list 8 years after the employee’s resignation, indicates that the duty of confidentiality has effectively entered a “lifetime validity” phase. Furthermore, the corporate fine for acts intended to take trade secrets overseas has been raised to a maximum of ¥1 billion JPY, and the threshold for “criminal prosecution → arrest” in malicious cases has been significantly lowered.
1. Organization of Legal Basis (In Order of Priority)
| Rank | Basis | Clear Validity Post-Resignation |
| 1 | Trade Secret under the Unfair Competition Prevention Act | ◎ (Criminal penalties and heavy civil liability) |
| 2 | Individual Confidentiality Agreement (NDA / Resignation Pledge) | ◎ (Strongest if explicitly written as “surviving post-resignation” in the contract) |
| 3 | Implicit Duty of Confidentiality under Work Rules / Employment Contract | ○ (Explicitly affirmed by precedents to survive post-resignation) |
| 4 | Duty of Good Faith under the Civil Code | △ (Subsidiary basis) |
2. Key Revisions and Trends (2024–2025)
2024 UCPA Revision (Effective July 2024)
- The statutory penalty for the crime of trade secret infringement was raised to “up to 10 years imprisonment or a fine of up to ¥20 million JPY.“
- The corporate fine was raised to a maximum of ¥1 billion JPY.
- Acts intended to take trade secrets overseas were explicitly included as punishable offenses.
- In practice, the threshold for “criminal prosecution → arrest” has been substantially lowered.
Impact of the Ministry of Economy, Trade and Industry’s (METI) “Trade Secret Management Guidelines” (2023 Revision)
- Courts have become extremely strict in judging “Confidentiality Management (秘密管理性).”
- Merely saying “it’s a secret” verbally is almost never sufficient.
3. Key Points to Note from Latest Precedents (2023–2025)
| Date | Court | Case Details | Practical Impact |
| Feb 2025 | Tokyo District Court | Former employee used customer list 8 years after resignation →Found to be a violation (approx. ¥210 million JPY damages). | Clear ruling that “the duty of confidentiality survives even after 8 years.” |
| Nov 2024 | Intellectual Property High Court | LINE and Slack conversation logs can also constitute Trade Secrets. | Chat logs must also be included in the scope of managed information. |
| Jun 2024 | Tokyo District Court | “Confirmation of Secret Return Document” was obtained upon resignation → Management was recognized, leading to criminal prosecution → arrest. | The importance of resignation documents has skyrocketed. |
| Dec 2023 | Osaka District Court | New employer silently acquiesced, knowing the employee was using “previous employer’s list” → New employer also held liable for joint tort with ¥50 million JPY in damages. | The new employer is also susceptible to lawsuits. |
4. “Most Dangerous Actions” in Practice Ranking (As of 2025)
- Taking customer lists/contact information (especially transcription to Excel or mobile contacts).
- Saving files to private cloud services such as OneDrive, Google Drive, or Dropbox.
- Mass downloads just before resignation (almost 100% detected by monitoring tools).
- Sales using “my own personal connections” while secretly using the list (which will be exposed).
- Uploading source code/design drawings to private GitHub repositories.
5. Essential Corporate Checklist for Resignation Procedures (2025 Edition)
| Item | Necessity Level | Notes |
| Individual Resignation Pledge (Explicitly stating duty survives post-resignation) | ★★★★★ | High risk of management being denied without it. |
| Forensic Investigation of PC/Smartphone (Using paid tools) | ★★★★★ | Almost all listed companies implement this in 2025. |
| Verification of Private Cloud Account Access Logs | ★★★★ | Possible with Microsoft 365/Google Workspace. |
| Confirmation of Secret Information Return/Disposal(Documenting specific file names) | ★★★★★ | The strongest evidence in court. |
| Monitoring for 6–12 Months Post-Resignation (Checking for transfers to competitors) | ★★★ | Increased use of detective agencies where necessary. |
6. Actions the Former Employee Must Absolutely Avoid (The Line for Criminal Charges)
- Physical data removal (USB, printouts).
- Uploading to the cloud and “intending to delete it later.”
- Calling customers at the new job while referencing the former employer’s list.
- Submitting a proposal that is identical to the former employer’s, while claiming it’s based on “personal experience.”
✅ Summary
The duty of confidentiality after resignation can now be considered “virtually lifelong.” Especially for information that qualifies as a Trade Secret:
- Liability can be pursued even after 10 years.
- Instances of criminal prosecution → arrest are rapidly increasing.
- The new employer is also liable for massive damages.
Conversely, if a company neglects “resignation documents + forensic investigation,” there is a high possibility of having to silently bear the damage, regardless of the extent of the loss. With proper measures, a company is almost 100% likely to win, and criminal proceedings are possible.
