Turning off the machine can be easily socially engineered around by a determined targeted attacker; all from fire alarms to a visit from IT staff to giving you

Turning off the machine can be easily socially engineered around by a determined targeted attacker; all from fire alarms to a visit from IT staff to giving you a free memory stick at a trade show and so on. If you were to be gifted a new USB keyboard tomorrow from some random company, you'd likely accept it unquestioningly. Also, given that you leave your computer unattended, even whilst turned off, gives the attacker opportunity to insert a small device out of sight, rather as cleaners really have done with keyloggers on computers at banks. Isn't when you are present the time when its hardest for them to attack because of the physical contact required? Of course, in films the robber-dressed-as-janitor always manages to walk into the server-room with a tool box.. There are three types of attacker, right? 1) your password/data is valuable, its a targeted attack, the attacker will take the risk of direct access to the machine; they can do this by socially engineering you to insert the trojan hardware, or they can add some small hardware dongle when you don't see or understand 2) law enforcement, they will grab the machine, you'll know they have done so; DMA attack is just a lot more straightforward than freezing it and probing type attacks. 3) those prepared to use a $5 wrench http://xkcd.com/538/ http://xkcd.com/538/