SWFUpload is an open-source JavaScript library that allowed users to upload files in WordPress. It was first used by WordPress in 2011 and was abandoned and replaced with Plupload in WordPress 3.3, released in 2011. It sure was replaced but WordPress still continued to bundle the library for plugins that didn’t migrate to Plupload. In 2013, the core team forked SWFUpload and maintained the project, applying security fixes submitted by the contributors.
And now, after six years of deprecation, the core team has finally announced that SWFUpload will be officially removed from WordPress core. The team first searched the WordPress plugin directory and then compiled a list of plugins that contain references to SWFUpload in their code. According to Western Ruter, the list contains around 128 themes and plugins on WordPress.org.
Among those 128 themes and plugins, below are some of the most popular plugins:
The team is working on a way to provide enough backwards compatibility to ensure there are no JavaScript errors and an upload form is displayed instead of Embedded Flash. Andrew Ozz also apologized to plugin authors noting that the list likely contains some “false positives”.
If you use one or more of the plugins mentioned above, then you are highly suggested to get in touch with the author and ask if it would function without SWFUpload in core.
Source: WP Tavern