Twitterr is a fake website/hijack website that lures off of typosquatting. It first locks the window so you can't close it. It then claims that your browser is infected with malware, and the website is an error with a flashing background. Some minutes later it then crashes all of the user's add-ons.
The website flashes white to black quickly creating, and repeats doing this, so people with epilepsy should be careful when typing.
The message appears to also be a fake message from Xfinity/Comcast.
This browser hijacking website only works on Google Chrome. On Firefox, the website redirects to Facebook's sign up site. On Safari, it redirects to a survey scam most of the time, but sometimes it redirects to a work-from-home scam, a lottery scam, or a search for "Twitter". It is currently unknown what happens in IE, Edge, or Opera.