Hacker News Reader

The messages come from your phone; that's why you need your phone to access the webapp.

I also use the web interface and I believe it tethers your phone to the browser - so the phone is sending the unencrypted messages to the browser window.

If you delete a message on the phone the message disappears in the web interface too.

Looks like you guys are right:

"WhatsApp Web connects to your phone to sync messages."

I.. did not know that.

It connects to your phone which stores the messages, I believe.