Safe QR code usage – how it stores data and how it can be manipulated

QR codes (Quick Response codes) are everywhere these days: on restaurant tables, parcels, posters, tickets, and business cards. They’re incredibly convenient — just scan with your phone and you’re instantly taken to a website, a digital menu, or even connected to Wi-Fi.

But how safe are QR codes, really? Do you actually know what data they contain, where they lead, and whether they can be tampered with or abused?

In this article, we explain how QR codes work, what kinds of data they can hold, the security and privacy risks they pose, how attackers exploit them, and how to use them safely as a user or developer.

1. What is a QR code and how does it work?

A QR code is a two-dimensional barcode that stores alphanumeric, binary, or special data. It was developed in 1994 by Denso Wave in Japan and is now an open standard used worldwide.

1.1 Structure of a QR code:

• Data area – contains the encoded information

• Position markers – three corner squares help the scanner orient

• Timing pattern – defines spacing between modules

• Error correction – allows partial recovery of damaged codes

• Quiet zone – empty space surrounding the code

1.2 What kind of data can it store?

• URLs

• Plain text

• Email addresses

• Phone numbers

• VCards (contact info)

• Wi-Fi credentials

• GPS coordinates

• Cryptocurrency wallet addresses

2. Where are QR codes commonly used?

3. Capacity and error correction

➡️ Higher error correction levels result in larger QR codes but greater resilience.

4. What are the security risks of QR codes?

4.1 Lack of transparency

QR codes don’t show their contents to the naked eye. A harmless-looking sticker could lead you to:

• Phishing websites

• Automatic app downloads

• Initiating calls or sending SMS

• Fake payment gateways

• Malware-laced files

4.2 QR phishing (quishing)

A newer phishing tactic where attackers place fake QR codes — on posters, menus, ads — that redirect users to malicious sites impersonating trusted platforms.

4.3 Physical tampering

Attackers may cover genuine QR codes with malicious ones, especially in public spaces like cafés, parking meters, or event venues.

4.4 Permission overreach

Some QR codes trigger actions such as:

• Launching a call or SMS

• Connecting to Wi-Fi

• Starting a file download

• Redirecting to app stores

5. How can QR codes be manipulated?

5.1 URL shortening

Attackers often use shortened links (e.g., bit.ly) to hide the destination of a QR code and prevent you from spotting suspicious domains.

5.2 Unicode tricks

QR codes can embed links with visually deceptive characters (e.g., www.paypaI.com using capital “i” instead of “l”) to spoof domains.

5.3 Malicious files

A QR code can link directly to a downloadable file — like a PDF invoice with malware or a .apk Android installer.

6. Real-world attacks

• USA, 2022: Fake QR stickers placed on parking meters redirected to fraudulent payment portals.

• Germany, 2023: QR codes in job ads led to infected .doc files with malware.

• Brazil, 2024: Fake Wi-Fi QR codes in cafés redirected users to phishing login pages.

7. How to protect yourself

7.1 For everyday users

✅ Don’t scan QR codes in public spaces unless you trust the source.
✅ Use QR readers that preview the link before opening it.
✅ Inspect domain names carefully — watch for typos or unusual characters.
✅ Never enter passwords or banking details on websites opened via unknown QR codes.

7.2 For businesses and developers

✅ Use HTTPS and a valid SSL certificate on target sites.
✅ Print the destination URL next to the QR code for transparency.
✅ Implement time-limited or one-time-use links.
✅ Protect physical QR codes from tampering (e.g., secure placement, watermarking).

8. How to generate secure QR codes

8.1 Recommended tools

• QR Code Generator Pro – advanced options, password protection

• qr-code-generator.com – reliable and easy to use

• Zint / qrencode (Linux CLI) – open source and terminal-based

8.2 Best practices

• Choose Q or H level error correction for resilience

• Avoid very long URLs — use custom domains when possible

• Never embed sensitive information directly in the QR code

9. The future of QR security

• Dynamic QR codes – change the destination URL without replacing the image

• Personalized QR codes – tied to individual users, valid for limited time

• Secure QR – watermarked, digitally signed for verification

• QR + Biometrics – layered authentication in mobile payments

QR codes are useful and widespread — but not inherently secure. Since users can’t visually verify what’s inside a QR code, they are vulnerable to manipulation and abuse.

The best defense is awareness. Understand what QR codes do, what they contain, and how to scan and share them safely and responsibly. Whether you’re a user or a developer, QR hygiene is an essential part of modern digital literacy.