Has anyone encounter Private Steam Messages from Malicious Hacked Accounts?

In the Imgur Provided https://imgur.com/a/PwWLtNl

Has anyone encountered these type of random private messages recently?
I am not friends with these people and somehow they are able to send these Messages which baffles me that I've contacted Steam Support Yesterday awaiting their response.

I've blocked around 10 people by now and wonder how are they sending these private messages and why now of all times.
Was there a Steam breach? A Steam Update or something that allows you to Message people who aren't your friends?

Incase of a Duplicated Thread if someone made one, please direct me there so I can learn more.

Edit: This is now quite alarming.

Edit 2: Thx to a Developer who posted here, this is how the Scammers/Hackers are able to exploit sending messages
https://github.com/poespas/steam-force-chat

Update by Steam Support on these Intrusive Message of Scammers/Hackers using the Github exploit.
Hey there,

Thanks for reaching out to Steam Support.

To answer your question, there's a couple of different ways for a user to send you a chat message if they are not your friend. The most likely method, would be if you are in a group chat, any user that is also apart of the chat will have the ability to send you a private message. You'll be presented with the message you saw in your screenshot and have the ability to block them before actually seeing their message. I can really only encourage you to use your best judgement when receiving these messages from non-friends. If you'd like some information how to avoid scammers moving forward, check out our Trade Scams article.

To address the github script you mentioned, unfortunately Valve / Steam is not affiliated with the website in question. As such we have no way of removing content from their website.

Finally, I want you to know we absolutely value feedback from the Steam community, and I'm forwarding your comments on to the appropriate department.

Additionally, I would encourage you to share any opinions, suggestions, or ideas with the community as well, by posting on the Suggestions/Ideas section of the Steam Discussion forums.

This forum is regularly read by Valve's development team.

Please let me know if you have any other questions and I'll be happy to assist you.

Steam Support

Everyone, we must voice our concerns at the Steam Forums.
https://steamcommunity.com/discussions/forum/10/
The Valve Team must acknowledge this problem.

You can also go through Customer Support and Reddit.

Edit: 3 Seems many Groups have made Announcement of these Suspicious Messages going through around and their Admins has been kicking members and reported them to Valve and Steam Community.