In a new attack, some websites have been set up to show visitors a slash page that says the vicim's computer has been blocked because is has been used to access illegal pornographic content. The user is then presented a link to pay an instant "fine" of $300 to the scammers.
This is a new variant of "ransomware". The most common of which is "fake AV". A fake anti-virus website or software will claim to scan your computer for free, then charge you to remove malware that it has "detected".
Details and screenshots here.