The bug, which is present in every version of Microsoft Windows from Windows 95 onward, allows an attacker to remotely take over and control a computer.
               
IBM Corp's cybersecurity research team discovered the bug in May, describing it as a "significant vulnerability" in the operating system.
               
"The buggy code is at least 19 years old and has been remotely exploitable for the past 18 years," IBM X-Force research team said in its blog on Tuesday.

Microsoft offers refunds for Office apps

After announcing Office app for free, Microsoft Corporation will now make refunds to users who have paid for the services.

The company said users of its Office suite of applications on Apple Inc's iPad would be able to create and edit documents for free instead of paying for a subscription, in a bid to capture more mobile users.

The move is the latest, and one of the most dramatic, in Microsoft's new strategy of getting customers to use their services regardless of device or operating system, rather than lose them to a proliferation of free or cheap alternatives.
               
The new strategy, led by new Chief Executive Satya Nadella, is a recognition that the dominance of Windows and Office on PCs has not translated to the fast-growing mobile arena, where Apple's phones and tablets and devices running Google Inc's Android rule.
               
Nadella's first major move after taking the helm in February was to make Office available on the iPad, which has attracted 40 million users.
               
By downloading a free app, users could read Office documents in Word, Excel and PowerPoint but had to buy a subscription, starting at USD 7 per month, to create or edit them. Now, that will now be free.
               
Microsoft also announced on Thursday it is releasing Word, Excel and PowerPoint apps for the iPhone for the first time, and rolling out a test version of those apps for Android tablets, which are expected to be released fully early next year.