“Zoombombing” is when uninvited guests join a Zoom meeting and cause distruptions. This can happen if a link to a Zoom meeting is shared to the public, and it can lead to a hurl of inappropriate content being shown to viewers in the meeting. There is also an automated tool being used to discover unprotected Zoom meetings (meetings without passwords).
Fortunately, there are a few things you can do to prevent uninvited guests and to make your meetings more secure, such as setting a meeting password, creating a waiting room, and more. Read the New York Times Article on how to prevent Zoombombing here.