Prevent certain tags from appearing in the [QUOTE] tag?

[dontpanic]

On our forums, I use a set of custom tags and that hide text not to be shown to a member until they reply to the thread. When using the reply with quote (the one inside the post, not below the thread) the entire post is shown, including what's inside these tags.

Is there a way to prevent this?

Sorry if this is the wrong location for this question.

Thanks!

[NTLDR]

This is otherwise known as the Lockdown hack and discussion of it here is forbidden.

https://vborg.vbsupport.ru/showthread.php?t=23500