Largest hacker convention

The largest hacker convention is DEF CON, an event that has been held in Las Vegas, Nevada, USA, every year since 1993. The most recent in-person edition of the convention, DEF CON 27 (held from 8–11 August 2019), attracted an estimated 30,000 attendees. The convention attracts a wide range of people involved in computer security including tech industry professionals, hackers, reporters, lawyers and cryptographers, as well as a plainclothes contingents from law enforcement, the military and various national security agencies.

The convention is best known for its many Capture the Flag (CtF) competitions. These are simulated hacking challenges in which teams attempt to reverse engineer dummy software, crack network security or decrypt information against the clock. These can either be "Red Team" competitions that pit the hackers against a secured target, or "Red Team/Blue Team" events, in which the target is being actively defended by another team of hackers. CtF events are routinely held by organizations within the computer security world, but the CtF events at DEF CON represent the highest level of competition in this sport.

In addition to the hacking competitions, there are also many other more typical convention events including presentations, speeches and seminars. These events are organized by groups of long-time attendees and staffed by trusted figures from the hacking community known as "goons". Many major computer security flaws and novel hacking techniques were first made public at DEF CON events. Other things to do (according to the event's FAQ) include "contests, movie marathons, scavenger hunts, sleep deprivation, lock picking, warez trading, drunken parties, spot the fed contests, and the official music events".

Tickets for DEF CON cannot be purchased in advance, and have to be paid for in cash to prevent attendees from being easily traced. In 2020 DEF CON was cancelled due to the COVID-19 pandemic, and replaced with online events known as DEF CON SAFE MODE.