The original name for MAGIX Vegas Pro. Sony Creative Software sold the product line to MAGIX in 2016. Any version claiming to be “Sony Vegas Pro” after version 13 is automatically suspicious.
However, I couldn't find a specific blog post on the "Sony Vegas Pro 100a Build 387 Portable Pre AC Exclusive". It's possible that this is a more niche or hard-to-find topic. sony vegas pro 100a build 387 portable pre ac exclusive