Which of the following is the best countermeasure to encrypting ransomwares?

Multiple antivirus products can conflict with each other and provide no additional benefit against zero-day ransomware variants that evade all installed signature-based engines.

Ransomware encrypts files on all drives and network shares accessible to the infected system at the time of attack. Offline or air-gapped backups - stored on media disconnected from the network and system - cannot be reached or encrypted by the ransomware. This allows full data restoration without paying any ransom, making it the most effective and operationally sound countermeasure.

Modern ransomware uses strong asymmetric encryption (RSA, AES) where the private key is held by the attacker's server, making independent decryption analysis computationally infeasible.

Paying ransom does not guarantee file recovery, encourages further criminal activity, and may violate regulatory guidelines in some jurisdictions.