I have spent like 15 minutes drafting a message to my client only to have my message expunged and see a nice notification:
The contents of this message may violate Upwork policy. Visit our Security page for more information.
Of course, the main content of the Security page does not even have the word "policy".
After some testing I fugered that the the reason Upwork didn't like the message was the link to an executable. I am a software developer. Why on earth should I be unable to send my Upwork clients executables, in links or even, dare I say, as attachments?
Also, dear Upwork developers - if my message violated some policy, just not let it through. Let me edit it before deleting it. Please.
The system is not perfect. Management has asked the developers to add many filters, but there is no way for the automated filters to differentiate between your innocence and someone else's maliciousness.
Use email, Slack or something else for your development-oriented communication.
We all know a few dozens of ways to transfer an executabe, but it's always best to use whatever the client feels most comfortable with, including the Upwork messenger.
I understand nothing is perfect but at least giving an option to edit the message instead of just deleting it would be a nice (and not too complicated) touch.