the forum is the best mechanism for that.
Just post something in the forum. That's it's purpose. To get that notification out to forum members.
when choice allow upload files to member register group.
risk : can inject rootkit or malware to my server.
solution : need a plugin scan av before upload files finish and store my server.
i research internet and found https://github.com/kylefarris/clamscan/blob/master/README.md
but i'm not develop and coder.
any develop can build new plugin scan av when upload files.
You can restrict what file extensions are allowed in the ACP.