Discord recently introduced logging in via QR code, which is pretty handy when the desktop version randomly decides to log you out.
However, as you may have noticed, a small exploit exists, so I'll say this upfront:
NEVER and I mean NEVER scan a QR code for Discord-related gifts or prizes, including Nitro giveaways, through the Discord mobile app, EVER. You are NOT redeeming the "prize", you're giving someone FULL access to your account, regardless of 2FA.
Until Discord adds a notice to their app, you'll have to be extremely cautious about this.
Be sure to spread the word to everyone you know. This is a serious flaw with Discord's login system, and there's probably a lot of people losing accounts to this scam.
AKA If you can't claim gifts via clicking, don't claim them.
OUR DISCORD SERVER WILL NEVER USE QR CODES - If you see them in this server, report it to an Admin or Moderator.