Tor / Tor Browser.

An anonymity network and hardened Firefox-based browser that routes traffic through three relays using onion routing to conceal user identity and destination. It belongs to the Attacks & Threats category of cybersecurity.

An anonymity network and hardened Firefox-based browser that routes traffic through three relays using onion routing to conceal user identity and destination.

Tor (The Onion Router) is a volunteer-operated anonymity network in which a client picks a circuit of three relays (entry guard, middle, exit) and wraps each packet in layered encryption that is peeled off relay by relay, so no single node knows both the source and destination. Tor Browser is a hardened Firefox ESR build pre-configured to use Tor, block fingerprinting vectors, and disable risky features. It also enables access to .onion hidden services that never leave the network. Tor is widely used by journalists, dissidents, and privacy-conscious users, but also by criminals running marketplaces and ransomware leak sites. For defenders, the relevant controls are Tor exit-node feeds, DNS sinkholing, EDR detection of unauthorized Tor clients, and DLP for outbound traffic.

Defences for Tor / Tor Browser typically combine technical controls and operational practices, as detailed in the full definition above.

Common alternative names include: The Onion Router.