That's because when someone tries to sign into your Instagram account on a device you've never used before, it will require them to enter a security code that is texted to your cell phone. This feature had been released in limited amounts to Instagram users previously, but now it should be available to all.
How to turn on two-factor authentication for Instagram:
1. Tap the Profile icon in the bottom row.
2. Tap the Settings icon. This will be a gear on iOS and three dots on Android.
3. Tap Two-Factor Authentication under Account.
4. Turn on the switch next to Require Security Code.
5. Tap Turn On. If you've never given Instagram your cell-phone number before it will ask you to do so now.
6. Enter the code sent to your cellphone and tap Done.
7. Tap Get Backup Codes.
8. Tap OK.
9. Tap Take Screenshot or Copy Codes to capture your codes. Store them somewhere safe (not in iCloud or on the top of your desk). If you lose access to your text messages or that phone number, these will be your only keys back into your account.
You've set up 2FA for your Instagram! Now you're practicing safe snapping.