Security is the degree of protection against danger, damage, loss, and crime. Security as a form of protection are structures and processes that provide or improve security as a condition. The Institute for Security and Open Methodologies (ISECOM) in the OSSTMM 3 defines security as "a form of protection where a separation is created between the assets and the threat". This includes but is not limited to the elimination of either the asset or the threat. Security as a national condition was defined in a United Nations study (1986)^{[citation needed]}, so that countries can develop and progress safely.

Security has to be compared to related concepts: safety, continuity, reliability. The key difference between security and reliability is that security must take into account the actions of people attempting to cause destruction.

Different scenarios also give rise to the context in which security is maintained:

Perception of security may be poorly mapped to measureable 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 security itself. For example, two computer security programs could be interfering with each other and even cancelling each other's effect, while the owner believes s/he is getting double the protection.

Bruce Schneier ( /ˈʃnaɪər/; born January 15, 1963) is an American cryptographer, computer security specialist, and writer. He is the author of several books on general security topics, computer security and cryptography, and is the founder and chief technology officer of BT Managed Security Solutions, formerly Counterpane Internet Security, Inc.

A son of Martin Schneier, a Brooklyn Supreme Court judge, Bruce grew up in Flatbush, attending P.S. 139 and Hunter High School. After receiving a physics bachelor's degree from the University of Rochester in 1984, he went to the American University in Washington, D.C. and got his master's degree in computer science in 1988. He was awarded an honorary Ph.D from the University of Westminster in London, England in November 2011. The award was made by the Department of Electronics and Computer Science in recognition of Schneier's 'hard work and contribution to industry and public life'.

In 1994, Schneier published "Applied Cryptography", which details the design, use, and implementation of cryptographic algorithms. More recently he published "Cryptography Engineering", which is focused more on how to use cryptography in real systems and less on its internal design. He has also written books on security for a broader audience. In 2000, Schneier published Secrets and Lies: Digital Security in a Networked World. In 2003, Schneier published Beyond Fear: Thinking Sensibly About Security in an Uncertain World.