Implanting malicious hardware

After reading this and this over at Bunnie's blog, I came to think that how easy someone can "implant" malicious hardware anywhere in the supply chain before the hardware reaches it's destination. Ball Grid Array chips are complex beast to work with physically. But, with the BGA reballing tool, even a complex chip like that could be replaced with ease (quote from Bunnie's blog):

Before seeing this, I was under the impression that reballing was an involved process, but with this jig the operator could strip and reball a chip in under a few minutes, which translates to a labor cost of a couple dozen cents

This is insane. In PC motherboard, the chipset is mostly in BGA packaging. Flash ROM chips these days are back in the old "DIP" (Dual In-line Package), so it's quite easy to work with. But, to think that even BGA chips could be altered with ease is just mind boggling.