Microsoft Corporation’s (NASDAQ:MSFT) Windows 10 launch kicked off to a strong start last week, with its usage share jumping by four times in just three days, reported, citing Irish metrics company StatCounter. Microsoft released Windows 10 Wednesday as a free upgrade for users who are currently using Windows 7 or Windows 8.

The increase was much larger than Microsoft’s last free upgrade of Windows 8.1 in October 2013.

The global Windows 10 usage share, a measure of how active users of the OS were on the Internet, doubled from 0.3 percent to 0.6 percent on the official launch day Wednesday, Irish metrics company StatCounter said. By Saturday, Windows 10's global usage share had climbed to 2.5 percent, Computerworld said.

Windows 8.1's usage share hit 0.6 percent on the third day after its debut, a fourth worldwide of Windows 10.

Microsoft announced millions of users upgraded in its first 24 hours of availability.

“While we now have more than 14 million devices running Windows 10, we still have many more upgrades to go before we catch up to each of you that reserved your upgrade,” Yusuf Mehdi, corporate vice president of Microsoft's Windows and Devices Group, said in a blog post Thursday.

However, researchers at Cisco Systems have warned users to beware of bogus Windows 10 upgrade emails from potential hackers. Cisco said the emails are designed to look like an official upgrade notice from Microsoft, but several words have random, out-of-place letters and punctuation.

Capture The email message above is a sample of the type of messages that users are being presented with. There are a couple of key indicators in the message worth calling out. First, the from address, the adversaries are spoofing the email to look like it is coming directly from Microsoft ( This is a simple step that tries to get users to read further. Photo: Cisco Blogs

The world’s largest software company posted quarterly earnings and revenue July 21 that beat Wall Street estimates. However, Microsoft was dragged down by a $7.6 billion write-down and restructuring in the company’s Nokia mobile-phone operation.

Despite the write-down, revenue for the company's commercial cloud computing, a crucial segment that includes Office 365 and Azure, grew 88 percent from a year ago. The world's largest computer software company is unexpectedly in a new phase of growth, thanks in part to solid revenue in its cloud business, despite global personal computer sales suffering their steepest declines in two years during last quarter.

“We believe the start of Microsoft's methodical launch of Windows 10 will be another stepping stone in Mr. Nadella's cloud vision taking hold, with the vetting process from developers/users providing valuable feedback from the field,” Daniel Ives, an analyst at FBR Capital Markets, said in a research note.

FBR Capital Markets maintained its Outperform rating on Microsoft with a 12-month price target of $53.

Shares of Microsoft have gained 9 percent in the last 12 months.