Back in 2007, Microsoft (NASDAQ:MSFT) made an investment in a new social media company called Facebook. The company has held onto it, and more than four years later you have to wonder if this is the greatest investment Microsoft CEO Steve Ballmer has ever made.

Don’t Miss: Google Dominates Mobile Advertising.

Microsoft invested “only” $240 million in Facebook, giving them a 1.6 percent stake in the company, according to GeekWire. At the time, it had a $15 billion value. Fast forward to the present and the two companies have built a solid, strategic relationship.

Some of their joint projects have included advertising initiatives and a collaboration between Bing and Facebook that puts Facebook data into its search results; this is something Google (NASDAQ:GOOG) is trying to do with its Google+ and Google search.

With Facebook’s impending IPO, Microsoft will get a better sense of its value with the company. Speculation for Facebook’s value has come in between $75 billion to $100 billion. For Microsoft this could mean a five to six times increase since its 2007 investment.

This comes in at more than a $1 billion investment for Microsoft…not too shabby.

Whether Microsoft holds onto the investment or sells it in the public market remains to be seen. But selling its complete stake could be a surprise given their strategic relationship. And let’s be honest, it’s not like Microsoft needs the money.

Investing Insights: Morgan Stanley Poised to Nudge Out Goldman for Facebook IPO Win.

Get Your FREE Special Report: 4 Things You Must Know About the US Economy Now!