Compromise system (via update mechanism or other things secured with SSL, VPN software clients, ...); use that to steal keys. I don't believe I've been a victi

Compromise system (via update mechanism or other things secured with SSL, VPN software clients, ...); use that to steal keys. I don't believe I've been a victim, and most of the ways you'd exploit this would leave enough traces to be high-risk-of-detection, I think. But, it's hard to prove a negative, so it's safer to act as if it had been compromised. (I'm also updating keys anyway, so this is just a matter of waiting a day or two to do so.)