John got a pop-up for the FBI MoneyPak scam. Leo says that's exactly what it is. The FBI doesn't sell a get out of jail free card for the cost of a MoneyPak card. Hackers, however, are making billions on it. Not only are they making money, they've locked up his computer as well.
Joe got bit by the FBI Moneypak virus. Leo says it's a well known ransomware exploit, and all viruses require the user to be complicit in the infection. So, Joe probably went somewhere or downloaded something that enabled the virus to get on his system. Unfortunately no repair can fully remove everything and it's likely what he tried just got rid of the notification and not the actual malware itself. That virus may have invited many other malware exploits to the party, too.