Thanks to a regulatory filing with the Securities and Exchange Commission (SEC), we now know that Microsoft has dumped its 7.26 percent stake in US cable giant Comcast. However, we don't know when this happened, what the software giant recouped from its investment, and why it has chosen to do so.

Microsoft could have sold its 150 million Comcast shares any time in the past year, so they could be worth anywhere from $2 billion to $3.4 billion, depending on the timing. The investment dates back to 1997, when Microsoft described the deal as part of its efforts to jumpstart broadband adoption around the US. Microsoft's initial investment was about $1 billion.

For its part, Comcast was going to investigate deploying Microsoft technology in its ubiquitous set-top boxes. During the past decade, Microsoft has rolled out product after product aimed at the living room, but Comcast has never deployed any of it broadly. In fact, today, Comcast customers can opt-into TiVo's digital video recording (DVR) solution, a competitor to Microsoft's Media Center software, for an additional fee each month. Comcast offers no Microsoft-supplied technology through its services anywhere in the US now.

All that said, it's unclear why Microsoft pulled its investment at this time, and neither Microsoft nor Comcast are willing to discuss the issue. But Microsoft is also apparently in the running to purchase Yahoo!'s search business again, and it's possible that the company wants to have as much cash on hand as possible. According to its most recent financial disclosure, Microsoft has about $9 billion in cash and cash-like assets.

The revelation comes just one day before the software giant is expected to announce less-than-stellar quarterly earnings and rumored sweeping layoffs for the first time in its history. Many expect Microsoft to lay off approximately 7000 employees, or about 7 percent of its worldwide workforce, and announce other cost cuts.