When ACID Pro 4.0 was released, copy protection was physical or simple digital authentication. You installed the software, typed in a serial number from the box, and you were done. However, in 2016, Sony sold its creative software suite (including ACID) to MAGIX. With the change in ownership, the old Sony servers that handled online activations and registrations were eventually repurposed or retired.
In 2016, the entire Sony Creative Software suite, including ACID Pro, was acquired by the German company . A critical discussion: What went wrong with ACID Pro 8 ? sony acid pro 40 serial number updated