Why did google security settings tell me my HTC Thunderbolt is not a very secure device?

A

AC Question

I recently smashed my Galaxy S4 and did not want to spend money right now on a new device. I dug out the Thunderbolt I used to use and had Verizon reactivate that hardware on my number.

Shortly there after in updating recognized devices in my Google account, it told me I'd have to change my security settings to allow the device since it's no longer provides the level of security current systems recommend. If I bought a used Galaxy s4, does that provide adequate security?