These things are never legit. It's scammers posing as the government. My dad got that same "MoneyPak" one a couple of weeks ago on one of his old XP laptops (if there's a wrong decision to be made on a pop-up, installer or UAC prompt, he'll usually make it). It's rather nasty in that it runs on startup and locks you out of Windows. The solution is to boot into Safe Mode (press F8 repeatedly when the computer is booting up) and use System Restore (Programs->Accessories->System Tools in XP) to roll your system back to before you contracted the malware.
... Or you could just remove it (in safe mode) from your startup entries and delete the infected exe's off your HDD (file scan for exe's created within the past few days). Most of the Ukash/other ransomware viruses are rather easy to remove.
Now, there's also a range of infections that are truly ****ed up, like the ones that start encrypting files on your HDD with a random keypass that you will never figure out. Those are nasty.