Ad giant WPP is fighting back against a lawsuit filed by one of its former executives, alleging that he improperly leaked sensitive trade secrets and client data that could jeopardize its business.

The lawsuit, from former WPP exec Richard Foster, accuses the company of retaliating against him and firing him after he raised concerns that the group’s media investment division was allegedly running an improper global kickback operation. In a new filing added to the case last week, Foster’s legal team included details of a purported investigation by WPP client Sony that said WPP had run a “fraud scheme” in China and other markets, in which it…