What type of malware is it that restricts access to a computer system that it infects and demands that the user pay a certain amount of money, cryptocurrency, etc. to the operators of the malware to r

Ransomware restricts access to a system or its data - typically through encryption - and demands a ransom payment, often in cryptocurrency, from the victim in exchange for the decryption key or removal of the restriction. This directly matches the definition provided in the question stem.

Riskware refers to legitimate software that can be exploited for malicious purposes but does not inherently restrict access or demand payment.

Adware displays unwanted advertisements to generate revenue for the attacker but does not restrict system access or demand payment.

Spyware secretly monitors and collects user information without their consent but does not restrict access or demand ransom.