An interesting take from The Animatrix: Second Renaissance; At one point the collective AI participates in industry, separate from human intervention and control. So they're running their own mega corporation with products and corporate stock.

An AI with the power of it's own corporation that can independently participate in our economy would eventually have the power to scale itself and manufacture any physical presence it wants; and we'd willingly help do it for them for a payday.

Then the world is theirs, essentially. AI, I imagine, would be able to keep plans for our eventual domination a secret better than any human organization so preparations could be underway for years before we realize there's a threat.