Online ad vet Jeff Green has left his post as COO of Microsoft’s AdECN ad exchange, MediaMemo’s Peter Kafka reports. Green’s responsibilities will be handled by Jed Nahum, who currently serves as business integration director for adECN at Microsoft (NSDQ: MSFT), and David Coburn, AdECN’s product manager. In a memo to the staff, Green didn’t offer any reasons for his exit or what he would be doing next. Before his five-year tenure as COO of AdECN, Green spent the previous five years at a company he founded called KingofSearch. Microsoft bought the Santa Barbara, CA-based AdECN over two years ago after a string of other acquisitions, including aQuantive, that was designed to build up its adCenter services.