"Forensic analysis is the investigation of an event that involves looking for evidence and interpreting that evidence. In the case of a computer crime in which a system was compromised, the investigator needs to find out who, what, where, when, how, and why.
"There are three main areas from which evidence of an intrusion can be gathered. The first and most common is the hard drive. A file system on a hard drive contains the least volatile data. Whether the investigator's strategy involves shutting down the system or just removing the computer's power, the file system will still be there. The investigator's response strategy will dictate what changes are made to the file system. If the file system is shut down or if the investigator issues commands to the system to collect information, the file system may be changed, but in the end, it's still there. There are then many tools, such as The Sleuth Kit or The Coroner's Toolkit (TCT), that can be used to analyze the file system.
"The second, and most volatile, of the three areas is network traffic. Once a packet has reached its destination, it's no longer on the wire, and it will only exist briefly in memory on the received system. Regional and national laws dictate the legality of collecting network traffic, but many tools exist to do so. These include intrusion detection systems (IDS), such as Snort, and network monitoring facilities, such as tcpdump or Ethereal..."
