Microsoft has taken steps to stop its security update for Windows being shared on file-swapping networks.
Legal warnings stopped the SP2 swapping
The SP2 update for Windows XP was being used by file-swapping activists to show how such systems can help get large, important files to lots of users.
But legal warnings from Microsoft have forced the file-swappers to end their experiment and stop making the software available to downloaders.
Now the only place people are able to get the update is from Microsoft.
A group of file-swapping activists called Downhill Battle put the SP2 update using BitTorrent peer-to-peer software to help Microsoft get the software to as many people as possible.
The SP2 update is intended to make Windows XP a much tougher target for virus writers and malicious hackers.
Microsoft has announced intentions to get the update on to 100 million machines in the next two months.
When it started sharing SP2, Downhill Battle said: "This project shows how file-sharing technology gives people without budgets or huge server space the power to solve problems themselves, without waiting for the government or some corporation to do it for them."
Pop-up ads blocked
Revamped firewall on by default
Outlook Express, Internet Explorer and Windows Messenger warn about attachments
Origins of downloaded files logged
Web graphics in e-mail no longer loaded by default
Some spyware blocked
Users regularly reminded about Windows Updates
Security Centre brings together information about anti-virus, updates and firewall
Protection against buffer over-runs
Windows Messenger Service turned off by default
The version being made available on the BitTorrent network was intended for corporations who have a lot of PCs to patch. A smaller consumer version of SP2 is due later this year.
When asked about Downhill Battle's action, a Microsoft spokesperson said: "The Microsoft Download Center site is the only authorized web source for downloading a licensed copy of Windows XP Service Pack 2.
"To report a website offering unlicensed copies of Windows XP SP2 for download, please send an e-mail to email@example.com."
According to the Downhill Battle website, Microsoft has now gone one step further and issued take down notices to two of the web hosts helping the group distribute the file.
The Microsoft action was apparently taken under the controversial US Digital Millennium Copyright Act
In a statement Downhill Battle said it had ignored threats like this before but decided to act on this one "because we started this site primarily as a demonstration and to that end it's already been a huge success."
Even though Microsoft has issued the warnings the SP2 file is unlikely to disappear from file-swapping systems as BitTorrent's structure makes it harder for firms to police what is swapped.
The legal action means that those wanting SP2 must now go to the official Microsoft site.
As well as letting people download SP2, Microsoft is also planning to let people order a CD with it on or get it via cover mounted disks on consumer technology magazines.