Just turn off the users connection
Instead of "hacking" the users data stream to insert a message via their browser(after some ignored emails), just turn off their connection.
And then Comcast should then do a instant call to the user stating why the connection is now dead and how to rectify it. And that does not break the Internet either.
In this screen shot by DSLreports,
How many people are going to try and verify the message? Scammers have used fake messages to scare people into clicking for a quick fix for some time. And got some really nasty infections from it.
I've read posts of Rogers cable internet hacking users data streams to insert ad's. Rogers makes blood money this way. And even have the ability to replace the actual websites ad's with Rogers ad's. And that is censorship. Which leads to not knowing if the website you are viewing(spoofed website) is the actual website that you want.
And never, ever allow a ISP to remotely access your system to 'fix' problems. There is no guarantee that they have any computer repair certification credentials. If they break your system, or delete important files, they will claim No responsibility for any damage.
Consumer Rights is more than just a suggestion.