The LG V10 seems to have a significant security vulnerability not shared by other devices with fingerprint readers. The bad news is that someone can add their fingerprint to your V10 without a PIN. The good news is that you have to unlock it for them first.
If someone gets their hands on your locked phone, they won’t be able to access it. But if you give it to them unlocked, to make a phone call or show off a photo for example, your phone is vulnerable. Normally, going into the fingerprint settings means entering your PIN.
But if you use a third party launcher and add an activity shortcut for adding fingerprints, you bypass the need for a PIN. You can add a fignerprint right away, letting you unlock someone’s phone at a later time.
Luckily, there’s an easy temporary fix. The LG V10 allows for a maximum of four fingerprints, so just fill all four slots and no one will be able to add another. This fix will work fine until LG patches the vulnerability.