According to a source with AllThingsD, the lawyers at Microsoft Corporation (NASDAQ:MSFT) and Facebook are duking it out over the hiring of Carolyn Everson. Everson was the global ad sales head and was hired as the VP of global sales at Facebook. Microsoft is considering blocking Everson from using any strategic information she learned while at Microsoft or from contact certain ad client companies on behalf of Facebook.

Facebook has poached Carolyn Everson, the head of Microsoft global advertising. Everson will be the VP of Global Sales at Facebook. Everson joined Microsoft last June itself. Everson will be replacing Mike Murphy and will report to David Fischer.