Fact does not come from the grand leaps of discovery but rather from the small, careful steps of verification. That is the premise of the Open Source Security Testing Methodology Manual also known as the OSSTMM (pronounced as "awstem") It is a peer-reviewed manual of security testing and analysis which result in verified facts. These facts provide actionable information that can measurably improve your operational security. By using the OSSTMM you no longer have to rely on general best practices, anecdotal evidence, or superstitions because you will have verified information specific to your needs on which to base your security decisions. One way to assure a security analysis has value is to know it has been done thoroughly, efficiently, and accurately. For that you need to use a formal methodology. The OSSTMM aims to be it.

via ISECOM – Open Source Security Testing Methodology Manual (OSSTMM).