Our server has a warning: "This server is using illegally downloaded software"

Okay, thanks. Ill try these and hope that it works.

... you can remove the plugins one at a time, or install one at a time. You already know a lot who is not suspicious...

never seen this last time it came in the middle of the screen but it was for vcmod

It probably means that you're using a protected leak like "Admin popups" when you restart the server it will say something about you server using leaks and it will not start up.
I'd say get a local host or a dev server and slowly put all your leaks onto the server until it starts happening again.
If you're not using leaks then I don't really know what to tell you :/

how do I remove the post limitation
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why do we have to reach 15 posts hhhhhhhhhhhhsbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

out the addons with encrypted strings to see if the message still appears, and it still appears.

We don't know how long this has been as we've only just noticed chat.
We would like to remove it so that players don't join, see the message and leave.
If we could simply change one of the a