Re: Touch ID

I have an iPhone 6S. Followed the Apple support page to set up Touch ID. Settings/Touch ID & Passcode/Add a Fingerprint. Successfully added Fingerprint 1 but then found by chance that any finger (mine) worked, not just the thumb that I set up with. So I asked my husband to try to open my phone with his thumbprint. And he did. Any digit worked. Asked a friend. Same thing. So I deleted the Fingerprint and re-installed it, thinking that would fix it but it still opens with any finger. So I deleted the Fingerprint altogether so there is now no fingerprint listed. And it STILL opens with anyone's finger or thumb. Not great security. How do I get around this? I'd be so grateful for any help. Thanks.