It is unlawful for a person directly or indirectly in connection with the purchase or sale of securities-

(a) to employ any device, scheme or artifice to defraud;

(b) to engage in any act, practice or course of business which operates or would operate as a fraud or deceit upon any other person; or

(c) to make any untrue statement of a material fact or to omit to state a material fact necessary with the result that the statements made in the light of the circumstances under which they were made, appear truthful.