The use of third-party tools to unlock devices can have legal implications. In many jurisdictions, unlocking a device is legal if the device's owner requests it, but using such tools for devices not owned by the person requesting the unlock can be considered illegal.
This "v40" version is marketed as a specialized utility that leverages alleged server-side vulnerabilities or iOS bugs to decouple a device from an existing Apple ID. icloud bug imei unlocker v40