Windows may be on more than 90% of the world's Personal Computers, but a growing campaign has taken to the streets to keep the Microsoft Operating System (OS) in its box.

Hundreds of people who prefer other operating systems, but had to buy Microsoft software with their new computers, converged on Microsoft offices on Monday.

Carrying shrink-wrapped manuals and disks and wielding the penguin mascots of the free Linux OS, they demanded their money back.

Windows Refund Day grew out of the Windows Refund movement launched in January 1999.

Like many Web-based phenomena, it has been propagated rapidly around the world by Net users and had official support sites in Japan, the Netherlands, France and New Zealand, as well as America.

In the most organised of Monday's protests, around a hundred users from the San Francisco Bay Area marched to Microsoft's offices in Silicon Valley.

While the protesters had been told the offices would be open, they were in fact closed for the Presidents' Day holiday. But Microsoft tried to defuse any bad publicity by serving lemonade and iced tea to the demonstrators in a nearby car park.

It was not issuing any refunds and urged the crowd to go back to the company that made their computers.

"You can buy a personal computer with a non-Microsoft operating system, you can buy a computer with no operating system at all. Most customers choose Windows but you certainly don't have to," said Microsoft spokesman Robert Bennett.

Linux users are most anti-Windows

Naturally, the refund-seekers support other Operating Systems, notably the free Linux open-source software.

According to the end-user licensing agreement that comes with PCs shipped with Windows, the user can request a refund if they do not agree to its terms. But this can mean having to return the whole computer to the manufacturer.

The Windows Refund Center Website advises a new computer should be unpacked, a boot disk for a non-Microsoft OS should be inserted, the machine then turned on and the new OS installed, before a request is made for a refund.

The site says some consumers do not like paying a "Microsoft tax" for any OEM (Original Equipment Manufacturer) software they do not want and have never used on their machine.

"This is only an issue because so many OEMs flatly refuse to sell a machine without Microsoft's OS on it. Some saying that their agreements with Microsoft require them to pay Microsoft for an OS for that machine, and to include one as well.

"Some OEMs even go so far as to say that they may not pre-load any non-Microsoft OS. We feel this is monopolistic, strong-arm, and restrictive of consumer choice," it says.

Australian pioneer

A number of people have managed to obtain refunds, many being inspired by the Australian Geoffrey Bennett who received A$110. He spent four months arguing by e-mail with Toshiba that he only had to return the software and not the computer. He eventually got his money back.

The campaign has yet to take root in the UK. A Microsoft spokeswoman at its Reading headquarters said there had been no reports of anyone turning up at Microsoft offices demanding a refund on Monday.