The Classic build has the old no longer developed MFC based UI, hence it lacks support for modern features, these features can however still be used when manually configured in the Sandboxie.ini. What's different is the user interface the Plus build has a modern Qt based UI which supports all new features that have been added since the project went open source. Both have the same core components, this means they have the same level of security and compatibility. Sandboxie is available in two flavors Plus and Classic.
