Karl Siebrecht, who was president of Atlas until parent company aQuantive was purchased by Microsoft (NSDQ: MSFT), is leaving Microsoft to join AdReady as the display advertising startup’s president. Kara Swisher first reported the news and Seattle area tech site TechFlash confirms it, with AdReady CEO Aaron Finn saying the hiring is indicative of the startup’s “progress.” Siebrecht most recently was a general manager at Microsoft, according to his LinkedIn profile. Swisher notes that former aQuantive CEO Brian McAndrews, who left Microsoft late last year, is now a managing director at Madrona Venture Group, which has invested in AdReady. We’ve reached out to Microsoft and AdReady for comment and will update when we hear back. Microsoft and AdReady both confirm the news.