How a simple three-digit number helps websites stick it to online censorship

Error 451 is an internet status code, a dull but necessary piece of the web’s architecture. These codes are like traffic signals: Whenever computers exchange information on the web they send each other codes, which essentially say things like “Got your request, I’m still working on it” (code 202) or “you won’t find that here, look there instead” (code 308). There are dozens of these codes, including the occasional gag (Error 418: I’m a teapot).