Tor (The Onion Router) is a network of around 7,000 volunteer-operated relays that anonymizes internet traffic by routing it through three relays, encrypting the payload in nested layers (the “onion”). Originally developed at the US Naval Research Laboratory in the mid-1990s, now maintained by the Tor Project, a US-based 501(c)(3) nonprofit. Free, open-source, and the most studied anonymity network in production.
What it means in practice
Each relay in the three-hop circuit knows only the previous hop and the next hop. The entry guard sees who you are but not where you are going. The exit relay sees where you are going but not who you are. Correlation requires controlling both ends simultaneously, which is the entire research field of “traffic analysis attacks” and the reason high-target operators use Tor over a VPN, or Tor with bridges, or Tor inside Whonix on Qubes. Tor Browser bundles the network with a hardened Firefox build that resists fingerprinting by making every Tor user’s browser look identical. Speed is the cost: typical exit-relay throughput is under 10 Mbps and latency adds 200 to 500 milliseconds per hop.
Who uses it, and against whom
Used by journalists to access whistleblower drop boxes (SecureDrop runs over Tor), by activists in countries where the open internet is censored, by domestic-violence survivors hiding research about leaving from a monitored device, by law enforcement for undercover work, and by ordinary users who do not want their ISP building an advertising profile. Adversaries are documented in the academic literature: nation-state agencies running large numbers of relays to attempt correlation (NSA, GCHQ, FSB), commercial chain-analysis firms targeting onion services, and sophisticated criminal exit nodes looking for cleartext credentials. Most users are not these targets and will benefit from Tor without those concerns being relevant.
What you can change today
Download Tor Browser from torproject.org (verify the PGP signature). Set the security slider to “Safer” by default, “Safest” for sensitive sessions (disables JavaScript globally). Never log into accounts tied to your real identity from Tor Browser, ever. For higher anonymity, run Tor Browser inside Tails on a USB stick, or on a separate physical device. If your country blocks Tor, configure bridges (obfs4 by default, snowflake or meek as fallback) from inside the browser settings.