The nine-year-old firm has offices in Shanghai, Beijing and Guangzhou and employs more than 270 people. Its iCast rich media ad-serving product has distribution agreements with all major portal and vertical sites in China.
HDT is also behind a video ad-serving product called iStreaming, which has distribution agreements with all major video sites in China; a contextual targeting advertising product iFocus; and the T2C advertising network, which has more than 200,000 sites delivering 150m page views a day.
The investment strengthen WPP's position in China, where it now employs more than 9,000 people, and is generating revenues of over $600m representing almost one-quarter of the company's Asian revenues.
In making its investment in HDT, WPP joins existing investors CA-JAIC China Internet Fund, Cheng Wei Ventures, Manitou Ventures and Sequoia.
The investment follows WPP's acquisition last week of a stake in a Scottish video games company Realtime Worlds, which is behind the Bafta-winning driving action game 'Crackdown'.