I've seen them.....usually they are "injected" into ads on sites, you'd never even knew.....it's the advertisers themselves not checking what kind of ads their clients are inserting.....
They typically are loaded with Javascript and will "mimmick" a Windows Explorer template, stating "Your computer is infected! Click here to Fix All Errors" as it proceeds to "fake" (act like it's scanning your computer) and detecting 100s of "viruses" - but in all actuality, there are NO viruses on the PC.....but the "software" that was just loaded when the user clicked "YES" to the User Account Control Prompt, "are you sure you want to run FBI Moneypak?"
Then there's usually a gimmick.....to "Fix" the "detected" files....you must "register" (I.e.: pay the ransom....money, CC, bank card.....) the product.
Apparantly a lot of suckers fall for it.....likely mooching off the elderly, teeneragers, and novice users.
But yes, between MalwareBytes, SUPERAntiSpyware, and Spybot S&D (in that order......and NOT all at the same time......) you should be all cleaned up....