Answer:
C) Blocking virus
Explanation:
It is true that money it is currently asked to be paid in cryptocurrencies like Bitcoin, but this malware existed before cryptos, so let's explain a little bit more about blocking viruses also known as ransomware.
A blocking virus restricts a part of the whole access to an operating system and also display the instructions to unlock it again, which is normally sending money to a specific account exaxtly as Astrid's case.