[Swordmaker]

with your computer off, they can power on your network card, upload software and have it open the mic and listen.

On a Mac, you have to specifically allow "Wake for network activity" otherwise it will not happen. Also, Apple has hardwired the camera light on iMacs and MacBooks so that if the camera comes on, the light will light. No software way to avoid that.

[sten]

i didn’t say the machine was waking up. just that you can power on the nic card

[Alvin Diogenes]

Also, Apple has hardwired the camera light on iMacs and MacBooks so that if the camera comes on, the light will light. No software way to avoid that.

That's not correct -- this has been broken in software:

Research shows how MacBook Webcams can spy on their users without warning (The Washington Post)

iSeeYou: Disabling the MacBook Webcam Indicator LED (Johns Hopkins University)

PDF of technical report on the above from Johns Hopkins Univ.

I don't know if Apple has plugged up the specific security hole these people used, but it was thought at the time that there was no way to do this because of the hardware interlock. This shows how clever techniques can do something that seems impossible.

A good rule of thumb is that if somebody thinks that something can't be hacked into, they just haven't thought about it hard enough or they don't know enough about the internals of the system. [And that's even ignoring the possibility of social engineering.]