The company has begun offering the final pre-release version of its upcoming Windows 7 operating system.
On Tuesday it pushed the Release Candidate build of the new Windows live for widespread user download.
Downloads will remain valid until 1 March 2010, when the operating system will begin shutting itself off every two hours in the run-up to the June 1 expiration date.
Microsoft is also encouraging users to back up their data before installing the update, particularly those running Windows XP or the Windows 7 beta, which require a 'clean install' of the update.
The release candidate is set to be the final version of Windows 7 released to testers before the company unveils the final retail version of the operating system.
Microsoft has officially set a loose target date of early 2010, though some vendors have claimed that the software could be out as early as October of this year.
Among the updates for the Release Candidate will be new security protections and a virtualised "XP Mode " for legacy software.