Microsoft Corp. acknowledged Wednesday that it needs to better inform users that its tool for determining whether a computer is running a pirated copy of Windows also quietly checks in daily with the software maker. The company said the undisclosed daily check is a safety measure designed to allow the tool, called Windows Genuine Advantage, to quickly shut down in case of a malfunction.

The tool, part of the Redmond company's bid to thwart widespread piracy, is being distributed gradually to people who have signed up to receive Windows security updates. The company expects to have offered it to all users worldwide by the end of the year.

Lazar said that so far, about 60 percent of users who were offered the piracy check decided to install it. Once installed, the program checks to make sure the version of Windows a user is running is legitimate, and gathers information such as the computer's manufacturer and the language and locale it is set for. That information-gathering is disclosed in a licensing agreement. But the agreement does not make clear that the program also is designed to "call home" to Microsoft's servers, to make sure that it should keep running.

At least every 90 days, the tool also checks again to see if the copy of Windows is legitimate. Lazar said that's because the company sometimes discovers that a copy of Windows that it thought was legitimate is actually pirated. When Microsoft believes a copy of Windows is pirated, the user begins to get a series of reminders that the copy isn't genuine. Such users also are barred from downloading noncritical updates, such as the new version of its Internet Explorer browser. But anyone who has signed up to automatically receive security updates, which repair flaws to prevent Internet attacks, will still get those fixes.

Update (June 28): Microsoft issued an update to its Windows Genuine Advantage (WGA) programme. The firm tweaked it so that your PC doesn't automatically report in to Seattle Central every time it reboots, like it did before. If you had auto updates set on your XP, you might never have realised this. Some people got a bit upset when they realised that, and so Microsoft relented. The Vole has even produced a page which tells you how to disable or uninstall the pilot version.