Installing leaked copies of Microsoft's Windows 7 operating system is highly risky.
Pirate versions of an early build of Microsoft's latest operating system are available on file-sharing networks.
Windows 7 is under final developer testing ahead of an expected commercial release later this month.
But security firm Fortify Software says there is no way of knowing whether or not hackers have tampered with the 2.44Gbyte file.
Anyone downloading and installing the operating system could find their PC generating malware, denial of service attacks and spam, said Fortify.
It is highly unlikely that any IT security application will protect users from internally coded malware in the operating system, said Rob Rachwald, director product marketing at Fortify.
"Fall-out from using an unofficial version of the new operating system could be quite severe," he said.
Windows 7, which is based on the code in Windows Vista, offers built in support for touch-sensitive displays.
In addition, Microsoft has extended its Bitlocker encryption technology to support portable storage devices.
Microsoft said users will also be able to connect securely to Windows Server 2008 networks without the need for a VPN.
