That probably explains why Yahoo shares are up 3% in after-hours trading. He’s resigning from the board — and related positions at Yahoo Japan and Alibaba Group Holding — 17 years after co-founding the company because “the time has come for me to pursue other interests outside of Yahoo!” he said in a letter to chairman Roy Bostock. Yang added that he’s “enthusiastic about the appointment of Scott Thompson as Chief Executive Officer and his ability, along with the entire Yahoo! leadership team, to guide Yahoo! into an exciting and successful future.” Bostock says that Yang “has always remained focused on the best interests of Yahoo!’s stakeholders, including shareholders, employees and more than 700 million users.” But his opposition to Microsoft’s 2008 acquisition offer of $33 a share still haunts him: Yahoo closed Tuesday at $15.43. Yang became CEO in 2007 when Terry Semel left, and in 2009 turned the top job over to Carol Bartz, who was fired in September. Investors complain that the company has floundered as Google became the dominant Internet search provider, and Facebook has grown into a major rival for display ads. Yahoo shares lost 8.2% of their value over the last 12 months, and are -47.6% over the last five years. In November, Daniel Loeb — who manages the Third Point LLC hedge fund, a major investor in Yahoo — called on Yang to resign amid reports that he was fighting efforts to find a buyer. The board is reviewing the company’s strategic options, but says that — for now, at least — it will remain publicly traded.