As an added (but unwanted) service, it appears that computer maker Dell is shipping motherboards that come pre-infected with a firmware-based trojan. Dell has confirmed that some of the firm's PowerEdge R410 server motherboards "contain spyware of unspecified function". "Dude, you're getting a Trojan!"
On one of their support forums, Dell states, "The potential issue involves a small number of PowerEdge server motherboards sent out through service dispatches that may contain malware. This malware code has been detected on the embedded server management firmware."
It 'll be very interesting to see just how and where the malware was placed into Dell's firmware, in large part because the firmware should have been tested for integrity before installation. And, if a major player like Dell can be compromised, how much easier would (will) it be to compromise smaller, less vigilant manufacturers?
The answer is, "probably very easy". It's likely that this is a trend that we'll see more of, since the benefits to the malware authors and distributors is huge. Think about it- shipping PCs with preinstalled malware cuts out the middleman and bypasses many of the roadblocks involved in getting malware on the PC in the first place. And since it's in firmware, detection is likely to be even more difficult.
As Ken Thompson would confirm, you can't be sure of anything unless you write the code and manufacture the chips yourself, and that includes ensuring that no step of the entire process is left unguarded. That would include writing your own compilers and the testing software that's used to make sure the end product hasn't been tampered with.
In other words, you'd have to create your own complete software industry and integrated circuit manufacturing plants from the ground up…which is as near to an impossible task as can be imagined. In short, unless you're in the loop 100% of the time and can make absolutely sure that no one is able inject modifications into any of the steps in the manufacturing process, you simply can't be certain that nothing was modified.