Maya's computer screen suddenly says that all files are now locked until money is transferred to a specific account, at which time she will receive a means to unlock the files. What type of malware has infected her computer?

The answer is "Crypto-malware".

Explanation:

It is a fairly recent concept that relates to program and malware component systems that have been created to take over the services of a device and use it for crypto-currency processing without direct user consent.

This malware is not intended to steal the data, but rather to remain secretly in location as long as necessary in the background. It is an Illegal encryption is a particular type of temporary victim device identification through the web, and other choices were wrong because it can't be defined in the given scenario.