I'm not a lawyer but it would be odd if a government agency couldn't communicate a possible threat to a tech company. It is in a company like LinkedIn's best interest to set up a phone number/channels for a centralized agency to communicate potentially malicious accounts and other emerging threats. I suspect that actually already exists for big companies. I doubt they are required to -do- anything without laws but this seems like a win that is easy for all sides. The problem is likely mostly on the US (and other govt) side of things. No clearly defined agency with a clear mandate, resources and leadership to take on this task.