Microsoft has seeded most consumer Windows 7 and Windows 8.1 PCs with an automatic update that will pitch the free Windows 10 upgrade to customers.

According to Myce.com, a March 27 non-security update aimed at Windows 7 Service Pack 1 (SP1) and Windows 8.1 Update -- the latter, the April 2014 refresh -- lays the foundation for a Windows 10 marketing and upgrade campaign. The update, identified by Microsoft as KB3035583, has been offered as "Recommended," meaning that it will be automatically downloaded and installed on PCs where Windows Update has been left with its default settings intact.

Microsoft was typically terse in the accompanying documentation for KB3035583, saying only that it introduced "additional capabilities for Windows Update notifications when new updates are available to the user."

Myce.com, however, rooted through the folder that the update added to Windows' SYSTEM32 folder and found files that spelled out a multi-step process that will alert users at several milestones that Microsoft triggers.

Computerworld confirmed that the update deposited the folder and associated files onto a Windows 7 SP1 system.

One of the files Myce.com called out, "config.xml," hinted at how the Redmond, Wash. company will offer Windows 10's free upgrade.

The first phrase, marked as "None," disables all features of the update. But the second, tagged as "AnticipationUX," switches on a tray icon -- one of the ways Windows provides notifications to users -- and what was listed as "Advertisement." Myce.com interpreted the latter as some kind of display pitching the upcoming Windows 10, perhaps a stand-alone banner in Windows 7 and a special tile on the Windows 8.1 Start screen.

A third phrase, "Reservation," turns on what the .xml code identified as "ReservationPage," likely another banner or tile that lets the user "reserve" a copy of the upgrade as part of Microsoft's marketing push.

Later steps labeled "RTM" and "GA" referred to Microsoft-speak for important development milestones, including Release to Manufacturing (RTM) and General Availability (GA). The former pegs code ready to ship to computer and device makers, while the latter signals a finished product suitable for distribution to users.

The upgrade won't be triggered until GA, according to the .xml file's contents.

Presumably, the messages shown in the tray icon -- and when displayed, the ad banner or tile -- will change at each phase, with the contents drawn from a URL specified by Microsoft in the .xml file.

Not surprisingly, the Enterprise editions of Windows 7 and Windows 8.1 -- those are sold only to large customers with volume licensing agreements -- will not display the Windows 10 upgrade pitches. That's consistent with what Microsoft has said previously, that the Windows Enterprise SKUs will not be eligible for the free upgrade. By refusing to show the alerts and ads to Windows Enterprise users, Microsoft avoids ticking off IT administrators, who will, by all accounts, stick with Windows 7 for the next several years before migrating to Windows 10 as the former nears its January 2020 retirement.

Although Microsoft has often prepped existing versions of Windows for upcoming updates with behind-the-scenes code, the extent of the messaging generated by the .xml file issued on March 27 would be a change from past practices. That fits with Microsoft's professed goal of getting as many as possible onto Windows 10, a position best illustrated by the unprecedented free upgrade.

Users will face a long line of nagging messages that will be impossible to ignore. Add to that the fact Microsoft set KB3035583 as Recommended -- by default Windows Update treats those the same as critical security fixes tagged "Important" -- and it's clear Microsoft will be aggressive in pushing Windows 10.

Those who don't want to see the Windows 10 marketing push on their machines can uninstall KB3035583 from the Windows Update panel. But because the .xml file was pegged as "version 1.0," there's a good chance more such updates will follow.