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ubbenMicrosoft shares rose 3.6 percent Monday to close at $30.83, the biggest single-day gain in more than a year, according to Bloomberg News. The main reason: This guy disclosed that he has invested a boatload of money in the company — just under $2 billion.

The investor’s name is Jeffrey Ubben, and he’s the founder and chief investment officer of ValueAct Capital, an investment firm that hasn’t been shy about pressing for major changes at companies where it holds large stakes. The disclosure of the investment appears to be raising hopes of some kind of major shakeup at the Redmond company.

Upon closer examination, however, Ubben isn’t exactly calling for Steve Ballmer’s head … at least not yet.

“In three to five years, which is our time horizon, we’ll stop talking about PC cycles and instead talk about Microsoft as the largest cloud-computing company in the world,” Ubben told investors at a conference today.

The Wall Street Journal notes that ValueAct’s stake amounts to less than 1 percent of Microsoft outstanding stock — not a position of significant leverage. However, Bloomberg notes that the investment appears to be ValueAct’s largest holding, which gives the firm lots of motivation to make sure Microsoft (or at least the stock) does well.

Microsoft tells the WSJ that its board and management “welcome the perspectives of shareholders.” The company says it is “committed to enhancing value for all shareholders, and will continue to take actions that we believe will enable us to achieve this objective.”

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