This FAQ article covers the QR code that can be displayed in the app (and is used to confirm a contact’s identity and add their Threema ID at the same time; green verification level), not to be confused with the QR code on threema.id websites (which can only be used to add contacts; red verification level).
Scanning QR codes is a means for confirming contacts’ identities. That way, man-in-the-middle attacks can be effectively prevented: If you receive a message from a confirmed contact (i.e., verification level 3), you can be sure that it wasn’t spoofed or read by a third party (provided said contact’s device wasn’t stolen or hacked). On top of that, scanning someone’s QR code is a convenient way of adding them to your contact list without having to manually enter their ID.
Display your own QR code
Navigate to the “My Profile” (Android) or “Profile” (iOS) tab and tap the QR code icon
Scan a contact’s QR code
Android: in the Contacts tab, tap the “New contact” button, and select “Scan ID”
iOS: Threema > Profile > QR-code icon in the top right corner
If you are having trouble scanning a QR code, please make sure the camera is not too close (below 10 in/25 cm), which might prevent it from focussing.
