I never knew this:
In general, if your debt is canceled, forgiven, or discharged for less than the amount owed, the amount of the canceled debt is taxable. If taxable, you must report the canceled debt on your tax return for the year in which the cancellation occurred. After a debt is canceled, the creditor may send you a Form 1099-C, Cancellation of Debt showing the amount canceled and date of cancellation.
In general, if your debt is canceled, forgiven, or discharged for less than the amount owed, the amount of the canceled debt is taxable. If taxable, you must report the canceled debt on your tax return for the year in which the cancellation occurred. After a debt is canceled, the creditor may send you a Form 1099-C, Cancellation of Debt showing the amount canceled and date of cancellation.