Cheeky software downloaders hoping to get a free version of Windows Vista are getting more than they bargained for - a password-stealing Trojan.

Security researchers Sunbelt Software have confirmed that the Trojan is contained in a program called "windows vista all versions activation 21.11.06.exe", which has been circulating on message boards, according to a report.

Windows Vista 'crack' installs Trojan

The program claims to be a "crack" designed to unlock pirated copies of Vista, which was made available to Microsoft's volume licensing customers last week.

It in fact installs malware known as Trojan-PSW.Win32.LdPinch.aze, which attempts to steal passwords and send them back to an attacker, according to security researchers Kaspersky, which first noted the Trojan in early October.

Users who have come into contact with the supposed crack have reportedly found that Norton Antivirus and Eset's NOD32 failed to detect the Trojan, though other anti-virus programs did stop infections from occurring.

Microsoft has said it expects Vista to see the fastest adoption of any operating system it has ever launched. Most analysts have taken a more cautious line, with many businesses saying they'll wait for up to two years before planning an upgrade.