Microsoft announced on July 18, 2006 that it had acquired privately-held Winternals Software. Terms of the acquistion were not made public.

Winternals is widely known for its invaluable commercial Windows tools, including
Recovery Manager , Protection Manager , Defrag Manager , and Administrator's Pak . The company is also widely known for its powerful freeware tools, many of which have long been staple components in security administrator's toolkits. The freeware, including Filemon, Regmon, Process Explorer and many others, are available at the company's Sysinternals Web site.

Writing in his blog, Russinovich said that "
millions of people use \[our tools\] every day for systems troubleshooting and management. There’s nothing more satisfying for me than to see our ideas and their implementation have a positive impact. That’s what makes being acquired by Microsoft especially exciting and rewarding."

Addressing concern about the future of Winternals and Sysinternals tools, Russinovich said that "some \[Winternals tools\] will find their ways into existing Microsoft products or Windows itself and others will continue on as Microsoft-branded products. As for Sysinternals, the site will remain for the time being while Microsoft determines the best way to integrate it into its own community efforts, and the tools will continue to be free to download." 

Winternals was founded in 1996 by Mark Russinovich and Bryce Cogswell. A spokesperson for Microsoft said that Cogswell will join the Windows Component Platform Team and Russinovich will join the Microsoft Platforms & Services Division. Russinovich, who is a senior contributing editor at Windows IT Pro Magazine, said he also plans to continue writing about Windows technologies.