Advertising giant WPP Group said WPP Digital, its digital investment arm, has bought a minority stake in Leading Smart, a BVI company, which has a controlling interest in the parent company of Moment Systems, the leading digital advertising measurement company in China. WPP didn't comment on the financial details of the agreement. Moment Systems was founded in 2006 in Beijing and currently employs 90 people.? ?"This investment continues WPP's strategy of developing its services in fast-growing markets and sectors and strengthening its capabilities in digital media," the group said. "Greater China - a region WPP has been committed to for over 20 years - remains one of the fastest growth markets for WPP," it added.