Tgtje's answer is correct. Let me provide some further information:
- You probably tried to install a plugin through your admin area ('Find plugins' section). This automatically downloads the plugin from e107.org and installs it onto your website.
- The plugin you downloaded is probably outdated and depending on its coding and your server settings, the copying of all the files to the right plugin folder may have been hindered. Simply said, there are some leftover files from the plugin download still located in your temporary folder.
- As a security measure, e107 checks which files are present. Sometimes, hackers try to upload malicious files. The warning you receive is a signal that something may be wrong. Seeing that these files belong to a specific plugin, it is safe to assume that these files are not malicious but simply leftover due to reasons I mentioned before.
- To resolve the warning, you can manually remove the files listed in the warning message. Downgrading to a lower version of e107 is not going to solve this issue, and is not recommended at all.
If you continue to have any issues, please visit us in the Gitter chatroom and we'll help you out: https://gitter.im/e107inc/e107