Microsoft, the world’s biggest software maker, is facing another major hack, this time on its servers.
The company’s cloud-based operating system, Windows Server, was affected by a software bug that infected Windows XP, a program Microsoft uses to distribute its software.
Microsoft said the malware is only found on computers running Windows Server 2003.
The bug, first discovered in March, caused Windows XP to crash, and it was found that the error could cause other systems to become infected.
The malware also infected some versions of Windows Server 2000 and Windows Server 2008.
Microsoft has warned its customers to avoid using the OS in their computers, but it did not elaborate on how it can prevent other computers from becoming infected.
Microsoft CEO Satya Nadella told reporters that it is a serious threat that affects millions of people, and that Microsoft will make a public announcement on Friday.
The problem could be fixed by Microsoft in just a few hours, Nadell said.
Microsoft told customers not to use Windows XP on their PCs because it can cause other computers to become vulnerable.
But the company is offering a free trial to customers who do not use Windows Vista or Windows Server 2007.
The free trial lasts for a week.
Microsoft’s cloud service, called Azure, runs on Microsoft’s computers and servers, and many users download the software from the company’s web site.
Microsoft is also offering free upgrades to Windows Server 2016.
The cost of the free trial is $19.99 per month, plus $2.50 per month for an annual subscription, according to Microsoft.
Microsoft will notify customers who register for the free Windows Server upgrade as soon as the software is available.
Microsoft does not provide an estimated number of affected PCs.
Microsoft did not immediately respond to a request for comment.
Microsoft, which has a reputation for keeping its customers informed, said customers should not use their computers until it is safe to do so.
The firm did not specify a time frame for when it will release updates to Windows, but the software giant is known for releasing patches and patches soon after they are fixed.
The Windows XP bug, which was discovered in December, was first discovered by Microsoft’s own internal security team.
That team found the bug in April, but its findings did not lead to any major changes to Windows.
Microsoft disclosed the vulnerability to the public, and the company did not notify users until Wednesday.
Microsoft says it will notify affected customers as soon the bug is fixed, but Nadello did not say how the company will notify them of the new vulnerability.
The vulnerability will not affect the free versions of Microsoft’s Windows and Office programs, but Microsoft says that users of those programs are at risk of being infected by the new malware.
Microsoft announced it is offering two free upgrades in response to the bug.
Users of Windows 8, Windows 8.1 and Windows 10 will receive free updates to their operating systems for a period of two years.
Microsoft customers who previously used the older versions of the software will receive the free upgrade, while those who previously installed Windows XP will receive a free upgrade to Windows Vista.
The Free Upgrade Program will continue to provide free upgrades through October, when Microsoft will provide the next wave of free updates, Microsoft said.
Windows XP has been a favorite of criminals and hackers, who have used the virus to steal sensitive information, including credit card numbers and passwords.
Windows Server has been the target of cybercriminals as well, and in March Microsoft revealed that it had detected a new variant of the virus.
Microsoft had previously disclosed that it was working on a fix for the virus, but in March it announced it would stop testing and release a patch for Windows XP.
Microsoft initially announced that it would release the new security patch in April after the company discovered the new variant.
Microsoft previously had announced that its fix would be ready for public release in May, but a week later, Microsoft halted the release of that patch.