Microsoft Corp released an emergency software fix on Tuesday after it learned that hackers had exploited a previously undiscovered security flaw in its widely used Office software to infect the PCs of its customers with tainted Word documents.
The software maker said on its website that it had released the software, known as a Fix It, as a temporary measure until it provides an update that will automatically patch computers to protect against the new threat.
Microsoft said that it had learned of a "very limited" number of attacks that exploited the newly discovered vulnerability, mainly in the Middle East and South Asia.
The company did not identify the victims, who received emails asking them to open the tainted Word documents.
The vulnerability affects customers using Office 2003 and Office 2007 as well as those running Office 2010 on Windows XP and Server 2003.
The attacks took advantage of an undiscovered flaw, or "zero day" vulnerability in industry parlance, which is usually only used on a limited number of high-value targets in a bid to keep the flaws a secret.
Typically, when makers of widely used software programs issue a warning about a zero-day bug, groups of hackers rush to reverse-engineer the Fix Its so they can build computer viruses that also exploit the same vulnerabilities.
Mr Stuart McClure, chief executive officer of the cybersecurity firm Cylance Inc, said that businesses using vulnerable versions of Office should install the Fix It to prevent attacks.
"I definitely think it is something that needs to be patched," he said.
Fix Its are pieces of software for remediating security flaws that must be manually downloaded and installed on PCs.
They are designed to protect customers while Microsoft prepares official updates, automatically delivered via the Internet to be installed on computers.
The new Fix It is available at this link: https: support.microsoft.com/kb/2896666