Microsoft Corp.'s Windows share of the internet connected computer market has dipped below 90 per cent for the first time, according to an internet-based measurement company.

In November, 89.5 per cent of internet users who connected to websites monitored by Net Applications Inc. used Windows as their operating system, a decrease of 0.84 per cent from October. The decline was the biggest in the past two years, the company said, and offset a number of recent gains.

Microsoft's decline was to Apple Inc.'s benefit, which saw use of its OS X operating system grow by 0.66 percentage points to 8.9 per cent in November.

Operating systems based on the open-source Linux platform, which make up only a sliver of the total market, also gained in the month, climbing from a share of 0.71 per cent to 0.83 per cent.

Net Applications linked Windows' decline to a similar decrease in the number of people using Microsoft's Internet Explorer web browser.

"The more home users who are online, using Macs and Firefox and Safari, the more those shares go up," Vince Vizzaccarro, the company's executive vice-president of marketing, told Computerworld on Monday.

Net Applications also found that Internet Explorer's market share dropped below 70 per cent for the first time in November. Rival Firefox ended the month with just over 20 per cent of internet users, with Apple's Safari coming in third with 7.1 per cent.

The measurement company said non-Microsoft operating systems and browsers fare better in months with fewer work days, since most business-owned computers run Windows while Apple and others are more common at home. The U.S. Thanksgiving holiday likely accounted for the better showing in November, Vizzaccarro said, which will likely be repeated in December through Christmas.