Pirated copies of Windows 7 have hit the shelves at China's electronics stores, months before the operating system officially goes on sale.

A stall owner at one of the multistory PC markets in Beijing sold a copy of the program. It was not clear from the thin, DVD-shaped box or the contents of the disc what version of Windows 7 it purported to carry, but a 1.8GB file named Win7.gho was on the' disc. A .gho file is an image of a system that can be copied onto a new hard drive, potentially letting a user bypass the activation key step for programs like Windows.

Both legal and cracked copies of Windows 7 were already available online. A release candidate version of the OS is publicly available, and subscribers to the Microsoft Developer Network can download the RTM (release to manufacturing) version on the network's website.

A cracked version of Windows 7 has also appeared online in recent weeks. An image file containing Windows 7 Ultimate RTM and a manufacturer product key was stolen from Lenovo and placed on a Chinese hacker forum, the company said.

A user can purportedly pair the leaked key with a certain hack to install and use the OS, Microsoft said in an MSDN blog entry. But Microsoft said it is working with Lenovo to make sure no PCs using the pirated manufacturer key are sold, and Lenovo said the key would be disabled. Windows 7 will go on sale on this year.