1. In infosec, availability describes the need that resources must be continuously available. For example, in the Kosovo war, the European forces bombed power plants in order to destroy the availability of electricity. Another example is in February of the year 2000, when massive DDoS attacks brought down major websites (making them "unavailable"). Controversy: Availability is one of the key sticking points in security. It is easy to secure things simply by making them unavailable: if a computer is turned off, nobody can hack into it. The trick to infosec is making things both available and secure. Examples of this problem are: account lockouts In order to prevent password grinding, computers will lock out accounts when too many bad passwords have been attempted. However, this means that hackers can purposely lock out accounts. firewalls and IDS Some IDSs will reconfigure firewalls, therefore spoofing attacks can cause the firewall to shut people out. fail-close/fail-open So called "proper" security will shut things down when things start to fail; for example, if the firewall crashes, it should shutdown all communication until the firewall is restarted rather than allowin traffic through unchecked. However, web-sites that demand 99.99% uptime are therefore unable to use traditional firewalls. Antonym: The opposite of the infosec term "availability" is the hacking term "DoS". See also: Availability is often mentioned along with other key security concepts such as integrity, authentication, confidentiality, and non-repudiation. From Hacking-Lexicon