"Work computers may have nefarious software on them. Computers which are shared with multiple people (think of a family) may have users who aren't as careful."

"Work computers may have nefarious software on them. Computers which are shared with multiple people (think of a family) may have users who aren't as careful." Even a computer you manage yourself could have nefarious software on it, as most people don't usually manage their operating system and the operating system provider could serve up malicious software (intentionally or unintentionally), either originally or in an update. Same with the hardware of the machine, which could also compromise your keys or grant unauthorized people access. I would not feel safe merely because I physically managed my own machines and knew something about security. Really, a computer needs to be completely offline and with no ability to get online. Safest is not to use a computer at all.