We have reports of this happening to a lot of people in-game right now as yet another attempt to get you to go to a site, so they can steal your login info and defile your characters.

Let's dissect the above whisper: 

It's one whisper made to look like two. This will work if your chat settings match the scammer's chat settings, but if you've fiddled with your font or chat window, then the formatting will be off and the scam will be more obvious. 

The whisper is from a garbage name. All "players" I've seen with random characters have been scammers or gold selling barkers. So anything after such a name should be considered highly suspect. 

It says [Game Master]GM. The scammers aren't even trying here. Blizzard GMs have names and have <GM> before their names. 

It sends you to a non-Blizzard site. Don't go to any website you get in tells or in-game mail as a general rule. If you have received a ban of any kind, you will receive an email to the account you have on file with your subscription info.