Security experts have urged users to be wary of pirated early versions of Microsoft's forthcoming Windows 7 operating system because they may contain malware.

An early build of Windows 7, labelled 'Windows 7 Ultimate Build 7000', was leaked onto the internet last week, and made widely available for download via several peer-to-peer networks.

Rob Rachwald, director of product marketing at security vendor Fortify, highlighted an increase in software infected with malware being posted on the internet, and warned that users should only download software from a trusted source.

"The whole idea is to exploit something popular, whether it's getting users to download porn or popular software. It's just a clever way to spread malware, " he said.

Rik Ferguson, solutions architect at content security vendor Trend Micro, echoed these sentiments.

"We would definitely discourage people from downloading and installing any software where they cannot be sure of the reliability of the content, or the trustworthiness of the source," he said.

"Pirated software distributed over peer-to-peer communities ranks pretty low on the credibility scale."

It is widely expected that Microsoft will make some significant Windows 7 announcements at the Consumer Electronics Show in Las Vegas this week.