Hangouts is a pretty convenient way to communicate. However, it has several disadvantages, one of which is privacy, because anyone can start a chat with another user, and nothing could be done. But Google is going to solve this problem.
The screenshot shows that in setting a new item «Setting permissions». The new item will allow you to specify different behaviors for people who have your phone number or email address. It is also possible to select the resolution for people who are not in your Google+ circles.
Settings for each case will allow people to contact you directly, send an invitation, or they can not contact you at all. Each category can be configured individually, so if you want to allow to contact you by phone number, but at the same time do not want to receive an invitation from someone who knows your an email, you can easily do it. Permissions item is now available in Hangouts, and no need to be updated.