What does a Virtual Private Network (VPN) primarily extend?

A Virtual Private Network (VPN) primarily extends a private network across a public network. This technology creates a secure encrypted connection over the internet, allowing users to send and receive data as if their devices were directly connected to the private network.

When a VPN is in use, the data transmitted between the user and the VPN server is encrypted, which helps protect against eavesdropping and ensures privacy. This capability is essential for remote workers or individuals accessing sensitive information over public networks, such as Wi-Fi in cafés or airports. The VPN essentially "tunnels" through the public network, providing the security and functionality of a private network.

The other options do not accurately describe the primary function of a VPN. For instance, extending a public network across a private network doesn't reflect the fundamental purpose of a VPN, which focuses on privacy and security. Similarly, extending a local network across multiple locales or extending a physical network across multiple services also do not capture the essence of what a VPN does, which is specifically about creating a private communication pathway over potentially insecure networks.