Many systems rely on keeping a master key secret. Sometimes this involves custom hardware and sometimes it relies on an implicit hardware property. And software writers tend to assume that hardware works in the intuitively obvious ways. But technological progress can undermine old assumptions. The upshot is that your laptop encryption software is no longer secure. The key used to protect disk files is typically kept in RAM, so a locked laptop can be unlocked by cooling it, interrupting the power, rebooting with a new operating system kernel, and reading out the key. This emphasizes once more the need for engineers who build security applications to take a holistic view of the world. Software alone is not enough; you need to understand the hardware, and the people too.