You need to send a bank statement to your accountant. Or a utility bill to a landlord. Or an invoice to a support team that asks, "which card was this charged to?"
They need to know which account. They don't need the whole number.
Why the Last 4 Digits?
Banks, card networks and receipts all settled on the same habit years ago: show the last four digits, hide the rest. •••• •••• •••• 4444 tells you which card was used. It doesn't let anyone use it.
The full number is what makes fraud possible. A full account number plus a name and an address is often enough to set up a direct debit, try social engineering against your bank, or match you across leaked datasets. The last four digits on their own are nearly useless to an attacker. They are still enough for a person to say "yes, that's the joint account, not the savings one."
What Usually Goes Wrong
Most people do one of two things:
Black out the whole number. Safe, but now the person on the other end has to write back and ask which account it was. That usually means you send the full number in a follow-up email, which defeats the point.
Leave it alone. "It's just my accountant." But the file gets forwarded, saved to a shared drive, or attached to a ticket in a system you've never heard of. Once a document leaves your hands, you can't control where it ends up.
There's also a third, sneakier failure: drawing a black box over a number in a PDF editor. Often the box sits on top of the text, and the number is still in the file underneath. Anyone can copy it out.
Partial Redaction in StripPii
StripPii 2.3 adds partial redaction. It's free for everyone, on Mac, iPad and iPhone.
- Add the document. StripPii finds the account numbers, card numbers, phone numbers and other personal details for you.
- In the review, tap a finding.
- Choose Keep last or Keep first. The rest of the value is covered, and the kept characters stay readable.
- Save a copy to share.
Account 9876543210 becomes Account ██████3210.
The covered part isn't just hidden under a box drawn on top. StripPii removes it from the saved copy, so nobody can copy the hidden digits back out.
One Thing to Check
The kept characters are read from the page and drawn back in. On a clean, typed document that's reliable. On a blurry scan, an 8 can be misread as a 3, and a wrong digit is worse than no digit. Give the kept characters a quick look in the review before you share. If a scan is too rough, untick the finding and draw a box over just the part you want to hide.
The Bottom Line
Share what the other person needs, and nothing more. For account and card numbers, that's almost always the last four digits.
StripPii finds and redacts personal information in PDFs, photos, text and Word files on Mac, iPad and iPhone. 100% offline: your files never leave your device. Download free from the App Store.
