This is specifically called "Ransomware," and is when an attacker holds the use of your computer ransom until a monetary sum is paid. I know you're already out some money, but I would consider having someone that specializes in virus/spyware removal look at your computer. Simply because they have restored functionality to your computer does not mean the malicious software has been removed, and your data could still be at risk.
As for the $439, if this was paid with a credit card, you should call the bank and attempt to cancel/chargeback the payment. They may push back, but I would be insistent that you were defrauded. Having filed a report with the relevant authorities may aid your argument with the bank, but I wouldn't expect much response outside of this. FYI - computer crimes are normally handled by your local FBI office and the Secret Service.
As for the Mac vs. PC debate, that's one that has been ongoing for a long time. Macs used to have an advantage in this field, as they were less prevalent and the economies of scale didn't make sense to write malicious code that targets them. However, as Macs have become more popular, there has been a notable increase in malware targeting that platform. The best defense is to be extremely cognizant of which files we execute (especially those contained in untrusted or unsolicited email), ensure your system has all updates installed, and to generally treat the Internet as an untrusted medium.
Hope that helps!
