At least for real estate contracts in the US, both parties have to initial each of the alterations and amendments to the contract that typically come up during negotiations. I doubt a random line crossed out in a contract would hold any legal weight in court unless acknowledged by both parties.

On the other hand, if I intentionally mislead you about the contents of a contract, it might not be binding. If you hand me a 10 page document, I pencil something in on page 7, sign it and hand it back to you without notifying you of the change, I don't thing you'd be required to honour my modifications.

Or you know, it might be fraud, as in the crime. Misleading someone about the contents of the contract they signed is exactly that. The paper (they printed) and gave to you in the understanding that you would sign and return it was altered in flight.

Essentially: if IBM wants you thrown in jail, you will be thrown in jail for this. Have fun in court.