Sending a quote to a partner, posting the result of a complaint on a bulletin board or sharing a customer inquiry with a colleague: a single piece of personal data left in a document can cause serious trouble. Here are the items to check before sharing and how to mask them safely.
Personal data you must check
Unique identifiers (most sensitive)
- Korean resident registration numbers and alien registration numbers
- Passport numbers and driver's license numbers
Processing these is strictly limited by law. They must never remain in a shared document as they are.
Contact details
- Mobile and landline phone numbers
- Email addresses
- Full street addresses
Financial information
- Bank account numbers and card numbers
Other identifying information
- A name combined with a date of birth, employee numbers, vehicle numbers and photos
The right way to mask
The principle is to keep the context you need and hide only what identifies the person.
| Item | Masked example | What is kept |
|---|---|---|
| Resident registration number | 900101-1****** | Date of birth and gender digit |
| Mobile number | 010-****-5678 | Carrier prefix and last digits |
| ho***@example.com | Domain | |
| Card number | 1234---3456 | Issuer and last digits |
| Name | Hong *-dong | Family name |
Keeping the last digits lets staff refer to "the customer ending in 5678". For public bulletin boards seen by anyone, hiding more is safer.
Common masking mistakes
1. Covering with a black box
Placing a black shape over text in a PDF or Word file does not remove the text. Moving the shape or copying the text reveals it. Change or delete the characters themselves.
2. Hiding Excel columns
Hiding a column or making the text white is not masking. The recipient can unhide it. Delete the column in the copy you share.
3. File properties
Document properties (author, company), comments and tracked changes can also contain personal data. Clean them up when you create the final version.
4. Catching only some formats
People often mask "010-1234-5678" but miss "01012345678" or "010 1234 5678".
Using an automatic masking tool
- Paste text into the privacy masking tool or drop an HWP, DOCX or Excel file.
- Registration numbers, phone numbers, emails and card numbers are detected automatically, with a count for each type.
- Formats with and without hyphens or spaces are all found.
- Copy the result or save it as TXT to share.
Because everything is processed in your browser, the original text is never sent anywhere before masking. Uploading the original to an external server just to mask it would defeat the purpose.
Final checklist before sharing
- No unique identifiers (registration, passport or license numbers) remain
- Phone numbers and emails are exposed only as far as needed
- I checked names and addresses that automatic detection does not catch
- I actually deleted data instead of hiding columns or covering it with shapes
- I cleaned up document properties and comments
- I asked myself again whether the recipient really needs this data
The last item matters most. The safest personal data is data you never send.