We examined whether acquisitions by Microsoft Corporation affect the stock prices of its competitors in the computer industry. We found that Microsoft's acquisitions in the Internet/online-services segment adversely affect the stock prices of the Internet/online-services rival portfolio. These competitors appear to be threatened by Microsoft's moves—anticompetitive or otherwise—to further its industry leadership and affirm the future success of the targets' technologies. Furthermore, the results of our study do not indicate that the financial market perceives Microsoft's operating-system acquisitions to be instrumental in achieving synergies from Microsoft's dominant role in the operating-system segment to the detriment of its Internet/online-services rivals. Indeed, we found the portfolio of Internet/online-services rivals to respond favorably to Microsoft's operating-system acquisitions, perhaps because Microsoft is essentially diverting resources away from the Internet/online-services segment.