1. Finance: A financing or investment instrument issued by a company or government agency that denotes an ownership interest and provides evidence of a debt, a right to share in the earnings of the issuer, or a right in the distribution of a property.
    Securities include bonds, debentures, notes, options, shares, and warrants but not insurance policies, and may be traded in financial markets such as stock exchanges.
  2. Banking: An asset pledged to guaranty the repayment of a loan, satisfaction of an obligation, or in compliance of an agreement.
    Security gives a lender or obligee a legal right of access to the pledged asset and to take their possession and title in case of default for a foreclosure sale.
  3.  Computing: The extent to which a computer system is protected from data corruption, destruction, interception, loss, or unauthorized access.
    See also secure system.
  4.  The prevention of and protection against assault, damage, fire, fraud, invasion of privacy, theft, unlawful entry, and other such occurrences caused by deliberate action. See also safety.

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Perception of security may be poorly mapped to measurable objective security. For example, the fear of earthquakes has been reported to be more common than the fear of slipping on the bathroom floor although the latter kills many more people than the former. Similarly, the perceived effectiveness of security measures is sometimes different from the actual security provided by those measures. The presence of security protections may even be taken for the safety itself. For example, two computer security programs could be interfering with each other and even canceling each other’s effect, while the owner believes s/he is getting double the protection.

Security theater is a critical term for deployment of measures primarily aimed at raising subjective security without a genuine or commensurate concern for the effects of that action on real safety. For example, some consider the screening of airline passengers based on static databases to have been Security theater and the Computer Assisted Passenger Prescreening System to have created adecrease in objective security.