"New Blackhole ransomware graphic mimics the FBI"
'...The malware, which claims to be a legal action by the U.S. Federal Bureau of Investigation (FBI), locks up the machine's Windows operating system and demands payment of a "fine" to unlock it.'
And yet another from the Internet Crime Complaint Center ((IC3) which states ...
'..the ransomware lures the victim to a drive-by download website, at which time the ransomware is installed on the user's computer. Once installed, the computer freezes and a screen is displayed warning the user they have violated United States Federal Law.'
You're no stranger to it, so there's no need for further descriptions.
The installation of ransomware requires a "user action". You may not want to hear it, but Malwarebytes' Anti-Malware Pro and Microsoft Security Essentials can't protect you against the actions you take. Or the choices you make. As Mark pointed out, do you take caution when visiting sites? Or clicking on links?
You asked how it can be stopped. I tend to doubt they will be. These sort of scams have been going on for years, in some form or another. Filing a complaint can only make a dent, but shining a light on it, might be a place to start.