How do you hide a forum without cancelling service?

While there is no literal way to hide a forum, here are a few advices that might help you better control the spam until you have a strategy in place:

  1. Disable new registrations
  2. Make forum read-only
  3. Require approval for new posts
  4. Require approval for new sign-up
  5. Make forum private

You can use any combination of the above options to temporarily avoid spam as your case may be.