The correct answer is Virtual Private Network (VPN) because it ensures that data transmitted over an unsecured network is encrypted and thus kept secure from interception. A VPN creates a secure tunnel for data packets to travel through an untrusted network, such as the internet, by encrypting the data before it is sent and decrypting it upon receipt.

Remote desktop is incorrect because it is a service that allows a user to connect to and control a computer from a remote location, but by itself does not provide encryption of data in transit.

File transfer protocol (FTP) is incorrect as it is used to transfer files between computers on a network but does not inherently provide encryption for data in transit.

Secure Shell (SSH) is incorrect because, while it does provide secure data communication through encryption, it is mainly intended for secure command execution and file transfer on remote computers, not for creating secure tunnels for general data traffic like a VPN does.