The correct answer is Software used to isolate a private network from a public network.FirewallSoftware is used to isolate a private network from a public network.A firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules.Firewalls have been the first line of defense in network security for over 25 years.They establish a barrier between secured and controlled internal networks that can be trusted and untrusted outside networks, such as the Internet. A firewall can be hardware, software, or both.Additional Information Computer virusA computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code.If this replication succeeds, the affected areas are then said to be "infected" with a computer virus, a metaphor derived from biological viruses.A computer virus is a malicious piece of computer code designed to spread from device to device.A subset of malware, these self-copying threats are usually designed to damage a device or steal data.Encryption KeyAn encryption key is a random string of bits created explicitly for scrambling and unscrambling data.Encryption keys are designed with algorithms intended to ensure that every key is unpredictable and unique.The longer the key is built in this manner, the harder it is to crack the encryption code.An encryption key is used to encrypt, decrypt, or carry out both functions, based on the sort of encryption software used.