This is indeed a nasty scam, but then scammers are inherently nasty, immoral people, so that's only to be expected. Even when they turn on the charm, it's all an act, based on the angle they take for their scam and the result they hope to achieve.
There was a woman on Scam Interceptors who was being scammed, when the team managed to find her and get in touch. The scammer, having spent a lot of time on their ruse, asked her to type her bank balance into her on-screen calculator - just so they could know how much to scam her for. It turned out that the woman didn't have very much money at all, so they just angrily exclaimed in their own language that it wasn't worth their time as they hung up on her - one of the interceptor team happened to speak the same language as the scammers.
One of the most bizarre ones that I had was supposedly from the Metropolitan Police, accusing me of having viewed/downloaded child abuse images - so not 'just' very embarrassing but otherwise legal activities, as in this thread. Obviously, if I had done the vile things that they claimed they had proof of, it would have been clearly illegal and very serious - but the Met was apparently happy to completely let me off everything if I just sent them several hundred pounds!
They did actually put a trojan on the computer - it was an old one that I was trying to set up and they got in there as soon as I got it online, a minute or so before I was able to instal the antivirus. It was quite a faff, but I managed to download a trojan killer on another computer, save it and then get it on to the old one.
Aside from all of the obvious lies that scammers make up, the thing to remember is that these are categorically not honest people. Whatever would make you think that, if you did pay them the money they're demanding, they would 'honour' their fake assurance and then leave you alone? They've found somebody foolish/vulnerable/terrified who will pay up what they demand, but these nasty criminals will then absolutely not dream of merrily trying to take you for more?!