It occurs to me that almost none of us could answer the question "did you pack it yourself" in the affirmative if we're using a PC, especially not if we bought it from a vendor who favors crapware.
I haven't actually had total control over the contents of a computer since I built a little box back in the 1980's that watched for a ring signal on a phone line, flipped the relay to pick up the line, used a 4 channel 8 bit A/D converter to sample 4 incoming voltages, then used a speech chip to speak the given voltages (in almost recognizable english) to the caller, twice, then hang up.
I wrote the code, programmed the 2764 EPROM, and it was totally under my control. I packed that piece of hardware... but since then... no way.
If you get a new PC from a good source, you can reasonably trust that the BIOS isn't going to be subversive. Once you load an OS, you've definitely had someone else doing your packing.
If it came loaded (or used)... there's really no way you can truly trust it, you just have to assume it's all going to be ok. Most of the time, it works out that way, or if it is a zombie on a botnet, you don't even know it, which is almost as good for most people.
It's a strange thought... but one I think might provoke some discussion.