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Many of the attendees at DEF CON include computer security professionals, journalists, lawyers, federal government employees, security researchers, and hackers with a general interest in software, computer architecture, phone phreaking, hardware modification, and anything else that can be "cracked." The event consists of several tracks of speakers about computer- and cracking-related subjects, as well as social events and contests in everything from creating the longest Wi-Fi connection and cracking computer systems to who can most effectively cool a beer in the Nevada heat. Other contests, past and present, include lockpicking, robotics-related contests, art, slogan, coffee wars, scavenger hunt and Capture the Flag. Capture the Flag (CTF) is perhaps the best known of these contests. It is a hacking competition where teams of crackers attempt to attack and defend computers and networks using certain software and network structures. CTF has been emulated at other cracking conferences as well as in academic and military contexts.
Conference founder Jeff Moss contends that the quality of submitted talks has diminished since DEF CON's inception because security researchers have found companies and government agencies to pay for the research, leaving the researchers less willing to unveil their zero-day vulnerability research "for free" at DEF CON. Additionally, the conference has gone from one track to five and accepting speaker proposals for five times the research lowers the density of "elite" speeches.
Since DEF CON 11, fundraisers have been conducted for the Electronic Frontier Foundation. The first fundraiser was a dunk tank and was an "official" event. The EFF now has an event named "The Summit" hosted by the Vegas 2.0 crew that is an open event and fundraiser. DefCon 18 (2010) hosted a new fundraiser called MohawkCon. In 2010, over 10,000 people attended DEF CON 18.
DEF CON was also portrayed in the The X-Files episode "Three of a Kind" featuring an appearance by The Lone Gunmen. DEF CON was portrayed as a United States government-sponsored convention instead of a civilian convention.
DEF CON was founded in 1992 by Jeff Moss as a farewell party for his friend and fellow cracker. The party was planned for Las Vegas a few days before his friend was to leave the United States, because his father had accepted employment out of the country. However, his friend's father left early, taking his friend along, so Jeff was left alone with the entire party planned. Jeff decided to invite all his cracker friends to go to Las Vegas with him and have the party with them instead. Cracker friends from far and wide got together and laid the foundation for DEF CON, with roughly 100 people in attendance. The term DEF CON comes from the movie WarGames, referencing the U.S. Armed Forces defense readiness condition (DEFCON). In the movie, Las Vegas was selected as a nuclear target, and since the event was being hosted in Las Vegas, it occurred to Jeff Moss to name the convention DEFCON. However, to a lesser extent, CON also stands for convention and DEF is taken from the letters on the number 3 on a telephone keypad, a reference to phone phreakers. DEF CON was planned to be a one-time event, a party for his friend, but he kept getting e-mail from people encouraging him to host again the next year. After a while, he was convinced to host the event again, and the attendance nearly doubled the second year.
A semi-fictionalized account of DefCon II, "Cyber Christ Meets Lady Luck" written by Winn Schwartau demonstrates some of the early DefCon culture.
In August 2007, 
MIT students Zack Anderson, R.J. Ryan and Alessandro Chiesa were to present a session entitled "The Anatomy of a Subway Hack: Breaking Crypto RFIDS and Magstripes of Ticketing Systems." The presentation description included the phrase "Want free subway rides for life?" and promised to focus on the Boston T subway. However, the Massachusetts Bay Transit Authority (MBTA) sued the students and MIT in United States District Court in Massachusetts on August 8, claiming that the students violated the Computer Fraud and Abuse Act (CFAA) by delivering information to conference attendees that could be used to defraud the MBTA of transit fares.
The court issued a temporary restraining order prohibiting the students from disclosing the material for a period of ten days, despite the fact the material had already been disseminated to DefCon attendees at the start of the show.
In 2008's contest "Race to Zero," contestants submitted a version of given malware which was required to be undetectable by all of the antivirus engines in each round. The contest concept attracted much negative attention.
WIRED reported that an ATM kiosk was positioned in the conference center of the Riviera Hotel Casino capturing data from an unknown number of hackers attending the DefCon hacker conference .
The director of the National Security Agency, Keith B. Alexander, gave the keynote speech. During the question and answers session, the first question for Alexander, fielded by Jeff Moss, was "Does the NSA really keep a file on everyone, and if so, how can I see mine?" Alexander replied "Our job is foreign intelligence" and that "Those who would want to weave the story that we have millions or hundreds of millions of dossiers on people, is absolutely false…From my perspective, this is absolute nonsense."
On March 12, 2013, during a United States Senate Select Committee on Intelligence hearing, Senator Ron Wyden quoted the 2012 DEF CON keynote speech and asked Director of National Intelligence James Clapper if the U.S. conducted domestic surveillance; Clapper made statements saying that there was no intentional domestic surveillance. In June 2013 NSA surveillance programs which collected data on US citizens, such as PRISM, had been exposed. Andy Greenberg of Forbes said that NSA officials, including Alexander, in the years 2012 and 2013 "publicly denied–often with carefully hedged words–participating in the kind of snooping on Americans that has since become nearly undeniable."
On July 11, 2013, 
List of venues and dates
- DEF CON 1 was held at the Sands Hotel & Casino June 9–11, 1993.
- DEF CON 2 was held at the Sahara Hotel and Casino July 22–24, 1994.
- DEF CON 3 was held at the Tropicana Resort & Casino August 4–6, 1995.
- DEF CON 4 was held at the Monte Carlo Resort and Casino July 26–28, 1996.
- DEF CON 5 was held at the Aladdin Hotel & Casino July 11–13, 1997.
- DEF CON 6 was held at the Plaza Hotel & Casino July 31 - August 2, 1998.
- DEF CON 7 was held at the Alexis Park Resort July 9–11, 1999.
- DEF CON 8 was held at the Alexis Park Resort July 28–30, 2000.
- DEF CON 9 was held at the Alexis Park Resort July 13–15, 2001.
- DEF CON 10 was held at the Alexis Park Resort August 2–4, 2002.
- DEF CON 11 was held at the Alexis Park Resort August 1–3, 2003.
- DEF CON 12 was held at the Alexis Park Resort July 30 - August 1, 2004.
- DEF CON 13 was held at the Alexis Park Resort July 29–31, 2005.
- DEF CON 14 was held at the Riviera Hotel & Casino August 4–6, 2006.
- DEF CON 15 was held at the Riviera Hotel & Casino August 3–5, 2007.
- DEF CON 16 was held at the Riviera Hotel & Casino August 8–10, 2008.
- DEF CON 17 was held at the Riviera Hotel & Casino July 30 - August 2, 2009.
- DEF CON 18 was held at the Riviera Hotel & Casino July 30 - August 1, 2010.
- DEF CON 19 was held at the Rio Hotel & Casino August 4–7, 2011.
- DEF CON 20 was held at the Rio Hotel & Casino July 26–29, 2012.
- DEF CON 21 was held at the Rio Hotel & Casino August 1–4, 2013.
- DEF CON 22 was held at the Rio Hotel & Casino August 7-10, 2014.
- DEF CON 23 was simultaneously held at Paris Hotel and Bally's Hotel from August 6-9, 2015.
- Black Hat Briefings
- Chaos Communication Congress (C3)
- Hack-Tic. 4-yearly European version
- Hackers on Planet Earth (HOPE)
- ToorCon. A yearly hacker conference held in San Diego, California since 1999
- Massachusetts Bay Transit Authority v. Zack Anderson, RJ Ryan, Alessandro Chiesa, and the Massachusetts Institute of Technology (United States District Court District of Massachusetts). Text
- Contest concept.
- Malicious ATM Catches Hackers | Threat Level | WIRED
- Greenberg, Andy. "Watch Top U.S. Intelligence Officials Repeatedly Deny NSA Spying On Americans Over The Last Year (Videos)." Forbes. June 6, 2013. Retrieved on June 11, 2013. "Eight months later, Senator Ron Wyden quoted[...]"
- Wagenseil, Paul. "Hackers Don't Believe NSA Chief's Denial of Domestic Spying." (Archive) NBC News. August 1, 2012. Retrieved on June 13, 2013.
- Whitney, Lance. "Defcon to feds: 'We need some time apart'." CNET. July 11, 2013. Retrieved on July 12, 2013.
- Blue, Violet. "Feds 'not welcome' at DEF CON hacker conference." ZDNet. July 11, 2013. Retrieved on July 11, 2013.
- "DefCon's Moss: Undercover Reporter Damages 'Neutral Zone'." Information Week. August 6, 2007.
- Mills, Elinor. "NSA director finally greets Defcon hackers." CNET. July 27, 2012.
- Official website
- CoffeeWars: 2007 Official contest
- The Alexis Park Resort & Hotel
- The Riviera Hotel & Casino
- A first ever look inside the DEF CON NOC (2008)
- The Story of DEF CON - video interview with Jeff Moss, a.k.a. Dark Tangent, the founder of DEF CON
- Transcript, audio, video of Jess Moss describing DEF CON's inception
- DEFCON: The Documentary