Microsoft is investigating the leak of an installation key that threatens widespread piracy of its forthcoming Windows Server 2003 software.

The Redmond giant has confirmed that the key, which found its way onto the web earlier this week, was issued to a corporate customer under its Volume Licensing Media programme.

It will work with the Standard, Enterprise and Web editions of Windows Server 2003.

Volume licensing customers received the Windows Server 2003 code on 4 April, the same day on which it was released to manufacturing. The new software is due for general release on 24 April.

A spokeswoman at Microsoft said that the rogue serial number is being treated as pirated software, and that users of it would find themselves locked out of updates and future service packs.

Bizarrely, she added: "Microsoft expected pirates to get hold of the Volume Licensing Keys at some point. So, in a way, it was all part of the plan."

But the company said that it would not employ technologies to try and cripple pirated installations when a user attempts to update the code.