The evil bit is a fictional IPv4

IPv4

Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...

 packet header

Header (information technology)

In information technology, header refers to supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission, the data following the header are sometimes called the payload or body....

 field proposed in RFC 3514, a humorous April Fools' Day RFC

April Fools' Day RFC

Almost every April Fools' Day since 1989, the Internet Engineering Task Force has published one or more humorous RFC documents, following in the path blazed by the June 1973 RFC 527 entitled ARPAWOCKY, which parodied Lewis Carroll's nonsense poem Jabberwocky...

 from 2003 authored by Steve Bellovin

Steven M. Bellovin

Steven M. Bellovin is a researcher on computer networking and security. He is currently a Professor in the Computer Science department at Columbia University, having previously been a Fellow at AT&T Labs Research in Florham Park, New Jersey.- Career :...

. The RFC

Request for Comments

In computer network engineering, a Request for Comments is a memorandum published by the Internet Engineering Task Force describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.Through the Internet Society, engineers and...

 recommended that the last remaining unused bit in the IPv4

IPv4

Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...

 packet header be used to indicate whether a packet had been sent with malicious intent, thus making computer security

Computer security

Computer security is a branch of computer technology known as information security as applied to computers and networks. The objective of computer security includes protection of information and property from theft, corruption, or natural disaster, while allowing the information and property to...

 engineering an easy problem — simply ignore any messages with the evil bit set.

Influence

The evil bit has become a synonym for all attempts to seek simple technical solutions for difficult human social problems, in particular efforts to implement Internet censorship

Internet censorship

Internet censorship is the control or suppression of the publishing of, or access to information on the Internet. It may be carried out by governments or by private organizations either at the behest of government or on their own initiative...

 using simple technical solutions.

The evil bit also became a noteworthy in-joke in Slashdot

Slashdot

Slashdot is a technology-related news website owned by Geeknet, Inc. The site, which bills itself as "News for Nerds. Stuff that Matters", features user-submitted and ‑evaluated current affairs news stories about science- and technology-related topics. Each story has a comments section...

. News about the publication of this RFC was posted in Slashdot dozens of times, reworded each time, among other April Fools

April Fools' Day

April Fools' Day is celebrated in different countries around the world on April 1 every year. Sometimes referred to as All Fools' Day, April 1 is not a national holiday, but is widely recognized and celebrated as a day when many people play all kinds of jokes and foolishness...

 stories, poking humour at the common criticism of Slashdot often posting duplicate stories.

As a joke, FreeBSD

FreeBSD

FreeBSD is a free Unix-like operating system descended from AT&T UNIX via BSD UNIX. Although for legal reasons FreeBSD cannot be called “UNIX”, as the direct descendant of BSD UNIX , FreeBSD’s internals and system APIs are UNIX-compliant...

 implemented this on the same day but removed the changes on the following day. A Linux patch implementing the iptables module "ipt_evil" was posted the next year. Furthermore, a patch for FreeBSD 7 is available and is kept up-to-date.

There is extension for XMPP

Extensible Messaging and Presence Protocol

Extensible Messaging and Presence Protocol is an open-standard communications protocol for message-oriented middleware based on XML . The protocol was originally named Jabber, and was developed by the Jabber open-source community in 1999 for near-real-time, extensible instant messaging , presence...

 protocol "XEP-0076: Malicious Stanzas", inspired by evil bit.

This RFC has also been quoted in the otherwise completely serious RFC 3675, ".sex Considered Dangerous", which may have caused the proponents of .xxx

.xxx

.xxx is a sponsored top-level domain intended as a voluntary option for pornographic sites on the Internet. The sponsoring organization is the International Foundation for Online Responsibility . The registry is operated by ICM Registry LLC. The ICANN Board voted to approve the sTLD on March 18,...

 to wonder whether the Internet Engineering Task Force

Internet Engineering Task Force

The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...

 (IETF) was commenting on their application for a top-level domain

Top-level domain

A top-level domain is one of the domains at the highest level in the hierarchical Domain Name System of the Internet. The top-level domain names are installed in the root zone of the name space. For all domains in lower levels, it is the last part of the domain name, that is, the last label of a...

 (TLD) – the document was not related to their application.

For April Fool's 2010, Google

Google

Google Inc. is an American multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its AdWords program...

added an &evil=true parameter to requests through the Ajax APIs.