I stumbled on Knoppix STD, and since I had used Knoppix (Linux that will run from CD), I was curious what the STD stood for. Don’t worry, it’s not contagious. It is a variation of Knoppix designed for security & forensics. I searched DistroWatch and discovered a few more distributions designed for forensics:
All but Helix are derived from Knoppix, but they’re all live CDs, so they can be used without installing anything on the computer, and they include tools to analyze (and hopefully fix) an ailing system.