They cannot be reverted once spent, they can absolutely be traced. Police can subpoena records from Moneypak, which is more than happy to comply. You also actually have to go out to a physical location, and swipe your Moneypak card, to buy something. That physical location will keep records, may have security footage, etc.
If you're doing Moneypak fraud, and live in any country with a funcitonal rule of law, it's just a matter of time until you either find yourself booked for processing, or, alternatively, ziptied, and with a brown bag over your head, put on a flight to the US.
Select quote: "In August 2012, the FBI also issued a warning that scammers were taking advantage of MoneyPak's untraceability to coerce unwitting victims into paying a "ransom" to unlock their computers infected with malware."