Digital forensics is the science of discovering and retrieving digital information from digital devices about an event in such a way to make it admissible in court to either prove culpability or innocent.
The goal of computer forensics is to perform a structured investigation while maintaining a documented chain of evidence to find out exactly what happened on a computer and who was responsible for it.
Forensic investigators typically follow a standard set of procedures: After physically isolating the computer in question to make sure it cannot be accidentally contaminated, investigators make a digital copy of the hard drive. Once the original hard drive has been copied, it is locked in a safe or other secure storage facility to maintain its pristine condition. All investigation is done on the digital copy.
The National Institute of Standards and Technology "Guide to Integrating Forensic Techniques into Incident Responses" covers four phases, which are briefly summarized below. For the complete 121-page NIST publication, download draft SP 800-86 at http://csrc.nist.gov/publications/nistpubs.
1 - Collection: Identify, label, record and acquire data from possible sources, while preserving the integrity of the data.
2 - Examination: Use manual and automated methods to assess and extract data of particular interest, while preserving the integrity of the data.
3 - Analysis: Use legally justifiable methods and techniques to derive useful information.
4 - Reporting: Describe actions used, explain how tools and procedures were selected, determine what other actions need to be performed, including forensic examination of additional data sources, securing identified vulnerabilities and improving existing security controls. Recommend improvements to policies, guidelines, procedures, tools and other aspects of the forensic process.