​(Image: ZDNet/CBS Interactive)

Microsoft's Get Windows 10 campaign is persistent, aggressive, and occasionally annoying. Annoying enough, in fact, to have spurred a cottage industry in third-party upgrade-blocking tools.

But despite those complaints, the program appears to be working.

Eight months after its launch, Microsoft says its new operating system is being "actively used on more than 270 million devices." Windows boss Terry Myerson made the announcement today at the opening of Microsoft's annual Build conference in San Francisco.

In his remarks introducing Myerson, CEO Satya Nadella said Windows 10 is "off to the fastest start in Windows history" and is being adopted at a dramatically faster pace compared to Windows 7 in the same timeframe, among both consumers and enterprise customers. Microsoft didn't offer any comparisons with Windows 8's adoption rates.

Today's milestone represents a major leap since the beginning of the year, when Microsoft announced that Windows 10 was in use on 200 million devices.

So what about that goal of having Windows 10 on a billion devices by 2018? Myerson said Microsoft is "on track to reach our ambitious goal of one billion Windows 10 devices in the next few years."

The free upgrade offer for Windows 10 has less than four months to go until its expiration date on July 29, 2016. Assuming that that offer isn't extended, the upgrade momentum will slow substantially beginning in the second half of 2016.

Microsoft's announcement today didn't break out adoption rates for enterprise customers. In January, the company said that 22 million of its active Windows 10 users were on devices run by enterprise or education customers. It's unlikely that proportion has changed substantially among notoriously conservative enterprise customers.

A relatively small number of those Windows 10 devices are Xbox One consoles and Windows 10 smartphones. But the real momentum for Windows 10 in the next few years isn't going to inspire such favorable comparisons to Windows 7.

The pace of PC sales has dropped substantially since its peak five years ago. There's also anecdotal evidence that PC owners are dragging out the replacement cycle. Microsoft says there are 600 million PCs in the installed base that are more than five years old.

That factoid led to an amusing war of words between Apple and Microsoft. At an Apple event earlier this month, Apple's Phil Schiller called that number "really sad."

Myerson's response: "We welcome everyone to Windows 10, whether you have a new PC, a five-year-old PC, or a brand new Mac."

Convincing those owners, especially enterprise customers, to upgrade is the real key to Microsoft's goal reaching a billion PCs running Windows 10.