Miscreants have brewed up a FBI-themed ransomware scam aimed at Apple users that relies on malicious JavaScript code rather than a conventional trojan.

The scam prompted a warning from the FBI-backed Internet Crime Complaint Centre on Thursday, and a denial that it was anything to do with the Feds. The ploy represents a further diversification for extortion-based malware, which has become a mainstay of the cybercrime economy over recent months and years.

Jerome Segura, a senior security researcher at Malwarebytes, came across the scam via a Bing Images search for Taylor Swift. This search led to a compromised site hosting an image mimicking police warnings.

The scam uses clever persistent JavaScript in its attempt to trick people into paying a supposed fine of $300 to "unlock their computers". Prospective marks are falsely told this is a "release fee" to avoid further legal consequences after they were supposedly caught "viewing or distributing prohibited pornographic content".

"Repeated attempts to close the page will only lead to frustration as even the 'Leave Page' browser trick does not work," Segura explains in a blog post. "If you 'force quit' the application, the same ransomware page will come back the next time [you] restart Safari because of the 'restore from crash' feature which loads backs the last URL visited before the browser was quit unexpectedly."

Users trapped in this vicious circle can escape by resetting Safari, he adds. A little web savvy means there's no need to give in to the extortionate - and bogus - threats of the scammers. However the sophistication of social engineering scam at play means that a few people, enough to make the scam worthwhile, are likely to be tricked into handing over money to fraudsters.

Although the scam most obviously takes advantage of the ‘restore from crash’ feature of Safari browsers on Mac machines it might just as easily be slung against Windows users. The scam uses black hat search engine poisoning tactics to targets users searching for popular search terms, which is how Segura came across it in the first place.

Finnish software security firm adds that although Segura was directed to an FBI themed webpage any European surfer would be directed to a Europol-themed fake warning page.

After the ransomware scam was exposed earlier this week the still-compromised webpages have been re-purposed to push traffic towards a hookup site. Although this particular campaign has been nipped in the bud the future appearance of similar scams along the same lines are all too likely.

"This scam is unfortunately all too efficient and is not going away anytime soon," Segura warns. It has posted a video tutorial on YouTube about how to remove the FBI ransomware on Mac OS X machines.

Earlier this week we reported how cybercrooks had grafted ransomware to a survey scam fraud. Victims PCs are locked up before slaves are pushed towards completing a survey in order to receive an unlock code.

The ransomware blocks Task Manager, CMD.exe, Regedit and the Start Menu from operating. The whole ruse is designed to enrich crooks via dodgy advertising affiliate networks, which take a relaxed line on marketing tactics that are illegal in many countries, including the US and UK.

It's since emerged that scams of this type first appeared in December 2012 if not earlier. Chris Boyd, a senior threat researcher at ThreatTrack Security, has posted an informative blog post charting the development of ransomware/survey scam hybrids since then here.

Boyd's post focuses on Shadowlock, one of the most sophisticated strains of ransomware/survey hybrid seen to date. News from earlier this week focused on an underground advert offering services relating to building survey launching PC hijacking ransomware. ®