ORDER OF VOLATILITY OF DIGITAL EVIDENCE

1. Not all information-based evidence is the same! Evidence can be organized into an “order of volatility” meaning how long it will stick around for you to collect until it automatically is lost.

2. Dan Farmer & Wietse Venema created the below table of evidence volatility, which is commonly referenced by forensic professionals. For example, information stored on a CD-R or some optical storage media can last for about 10-100 years depending on the brand used. Information stored in a computer’s main memory, by contrast, will last for only tens of nanoseconds before it is wiped out by the computer’s normal processing.

TYPE OF DATA	LIFESPAN
Registers, peripheral memory, caches, etc.	Nanoseconds or less
Main memory	Ten nanoseconds
Network state	Milliseconds
Running processes	Seconds
Disk	Minutes
Floppies, backup media, etc.	Years
CD-ROMs, printouts, etc.	Tens of years

3. Very critical from forensics point of view.....most people would want to turn a computer off (or at the very least unplug it from the network) when they realize an incident has occurred. However, as noted in the chart above, one will lose evidence in main memory and “network state” information (which other systems the computer is connected with and what information they are exchanging) with such an approach. Even shutting down a computer the “normal” way (Start / Turn Off Computer / Turn Off in Windows XP) can delete evidence, as Windows performs a number of housekeeping tasks in the shutdown process, such as closing opened files and clearing out the temporary disk cache.

4. Thanks Peter C. Hewitt (Read from Browser Forensics).