This article will highlight how you have to be careful about settings when you make some content available publicly, like Groups or Drive file.
The original article describe how an external person of the domain can subscribe to your Slack company channel by using a Google Groups that is publicly accessible. Stéphane Giron’s article helps answer the question – how to prevent and how to identify if some groups are concerned.
Source: GGvulnz — How to check your domain and groups settings