We have seen that one must be prepared to make sacrifices so that the laws of forbidden speech not be violated.
In the world of business, when one’s product is maligned by competitors, the natural and predictable reaction is to repond in kind. Such is not the way of the Torah. There is no basis for the notion that one who has been the object of loshon hora can respond with a counter-offensive of defamation.
Sefer Chofetz Chaim, 10 Cheshvan, pge 128