Microsoft's efforts at making life difficult for pirates of its flagship Windows XP product have been thwarted yet again.

With the release of XP Service Pack 1 three days ago, the Redmond giant warned people using pirated versions of the operating system that they would not be able to install the upgrade.

But the pirates were one step ahead yet again, releasing a tool that could beat the protection system even before the service pack was available for download.

One techie site, Tweak Town, put up a downloadable tool and a guide explaining how to get round the 'obstacle' of being prevented from installing the upgrade.

"Let's face it, these users are already running an illegal copy of Windows. Can further harm really be done?" the website said.

"Depending on how you look at it, there are two answers to this question. Let's continue anyway, even with the possibility of Microsoft pulling a knife to my throat."

The crux of the security measures in Service Pack 1 are based on the fact that the upgrade refers to a list of product keys which Microsoft has blacklisted.

These few keys are used by the majority of pirates to get their bootleg copies of XP registered. If the service pack is installed on a machine using one of these keys, it will terminate the process.

But a serial key changer program effectively allows illegitimate users to change the serial key on their installation to one that is not blacklisted.

Service Pack 1 will then install without a glitch, allowing pirate users to benefit from the latest tweaks and security updates.

When made aware of the situation, Microsoft claimed that security in the service pack, as in XP, was "never designed to protect the product against the serious hacker. Its intent was just to curb casual copying."

The company said that a little security should put off the majority of bootleg XP users, but acknowledged that there would always be a few hardcore hackers who get through.