And even when the OS detects that existing AV software hasn't been updated recently, it will only offer Windows Defender as one of several choices.
When the PC stops receiving AV signature updates -- most likely because the trial version has expired -- Windows 8 begins a 15-day countdown. During those 15 days, the Action Center, a desktop component that consolidates important system notifications, will warn the user that the AV software is expired, with information about how to renew coverage.
After the 15 days, the warning will expand the options offered users.
"At the end of 15 days the user has the option to renew what they have, install Windows Defender, select another option from the Microsoft Store or click on a 'remind me later' button, which starts a seven-day notice period," said Davis.
The Microsoft Store is the name of the company's online market, where it sells its own Windows software, including operating system upgrades, as well as some third-party programs. It's not to be confused with the Windows Store, the e-mart accessible only from Windows 8 that is the sole distribution channel for Metro-style apps for that OS and Windows RT.
Currently, the only AV software sold in the Microsoft Store is from Trend Micro, which along with McAfee and Symantec, are the three largest antivirus firms.
Although Windows 8 users will be notified during the 15-day span -- and after that if they take no immediate action -- the protection gap will put those PCs at greater risk of cyber attacks and malware infections.
Not that those computers won't have company: Last week, McAfee cited a year-long study and claimed nearly 20% of U.S. Windows PCs lack any active security protection. More than a third of those machines had expired AV software on their hard drives.
Microsoft's decision to hold off on activating Windows Defender in Windows 8 is in line with its approach to securing older versions of Windows. In late 2010, Microsoft began offering Security Essentials to Windows XP, Vista and Windows 7 PCs via the company's Windows Update service. Since then, Security Essentials has been listed as an optional download from Windows Update only on PCs that lack other working AV software, a category that includes present-but-expired third-party programs.
At the time, Trend Micro called Microsoft's move to use Windows Update to offer the free Security Essentials "unfair," and said it "raises significant questions about unfair competition."
AV vendors have butted heads with Microsoft several times.