They're stored in "plaintext" on the computer that the activation data is on. (It's cryptographically signed, so it can't be modified, but it's readable from someone with moderate skills).
On TurboFloat when the client station ask for a "custom license field value", is it passed in clear in the TCP protocol?
Currently (v3.5.6), yes. We assume TurboFloat / TurboFloat Server are on a closed network. We know that's not always the case, which is why in an upcoming version all traffic will be encrypted by default. It won't be the next version, but soon after.