I've heard of this occurring in other places near me, and plenty in K-12 sites in the US, but no direct experience - thank God.
With anything like this - if you can restore from backup then do so, even if it means losing some work.
Please don't pay.
It does leave something behind to prevent re-infection - and would you really trust that computer agajn, knowing that it has been compromised and not totally cleaned up?
Tom