If you’re a Mediacom customer and subscribe to their Internet service, you may get an HTML message injected into whatever website you visit. They are somehow able to insert their own HTML into whatever site you are viewing. Below is a screen shot showing what this looks like, and here is the actual text of the message:
IMPORTANT: From 4/19/2016 04:00 AM to 4/19/2016 06:00 AM (Central Time) we will be performing maintenance on our Internet systems network. For this reason, during this time, your connection to the Internet may be unavailable or slow. Our maintenance program involves regular system updates and improvements that help make your service experience more reliable and deliver the always fast Internet you expect from us. We apologize for any inconvenience this may cause you, and appreciate your patience and understanding while we work to improve your service experience.
The example below is what a person would see visiting a site like Subaru.com. The message would appear above the website content.