1. Open WhatsApp on your computer or visit web.whatsapp.com on your computer. (Make sure it is the official client or website)
2. When prompted with a QR code, use the QR scanner within WhatsApp to scan the QR code.
3. To do so, open WhatsApp on your phone.
   
   • On Android: in the Chats screen > Menu > WhatsApp Web.
   • On iPhone: go to Settings > WhatsApp Web.
   • On Windows Phone: go to Menu > WhatsApp Web.
4. Scan the QR Code on your computer screen from your phone.

To logout of desktop from WhatsApp

1. Go to WhatsApp on your phone > Go to Settings or Menu.
2. Tap on WhatsApp Web.
3. Tap Logout from all computers.

If you believe someone has scanned your QR code and has access to your account via WhatsApp Web, use the instruction above to log out of all your active web sessions in WhatsApp on your mobile phone.

Note: If you are unable to scan the QR code, ensure that the main camera on your phone is functioning properly. If the camera is not able to auto-focus, blurry or is broken, you may not be able to scan the barcode. Currently, there is no other way of logging into WhatsApp on your desktop.