I don't think they randomly spam, but sometimes when you login to Google+ it will show you a large window of all your google contacts that are not in your circl

I don't think they randomly spam, but sometimes when you login to Google+ it will show you a large window of all your google contacts that are not in your circles with an easy way to invite all of them. It's easy to accidentally click the button to send invites just to close the window and it's also easy to not realize who all you sent them to.