Spam is the bane of our lives, even moreso now that we're all online and bots can be programmed to abuse any system that allows people to generate content and where other users read and consume said content. So is the case with Google+ communities. If you're starting your own community and you expect it to be popular, you're probably dreading the amount of spam that you'll have to deal with just to keep things rolling like they should.
Now Google+ has its own content control system on the web, Android, and iOS that checks posts for questionable content and flags them for the moderator to manually accept/reject them. The toggle is already live in Google+ 7.6 so it's likely a server-side switch that is being flipped on for users.
It's turned on by default when you try to create a new community and it should also enable itself by default in your previously created communities. Check it out and make sure it's set on if you want to save your community from the annoying spam messages that get submitted to it.