Affects all versions of Word.
A bug in Word that was apparently being used to try to steal banking logins will be patched, Microsoft has said.
The previously undetected, or "zero-day", vulnerability had been reported over the weekend.
Then, on 10 April, cybersecurity firm Proofpoint announced it had discovered an email campaign targeting the bug that aimed to distributed Dridex malware.
Dridex is designed to infect a victim's computer and snoop on banking logins.
In 2015, it was cited as the means by which cyber-attackers stole more than £20m from British bank accounts.
The flaw discovered in many versions of Microsoft Word for Windows could allow malicious software, including Dridex, to be installed, according to cybersecurity researchers.
A scam email campaign was found to be distributing Microsoft Word RTF [Rich Text Format] documents to recipients that contained Dridex.
"During our testing (for example on Office 2010) the vulnerable system was fully exploited," wrote Proofpoint researchers in a blog.
"We plan to address this through an update on Tuesday April 11, and customers who have updates enabled will be protected automatically," said a Microsoft spokesman.
"Meanwhile we encourage customers to practise safe computing habits online, including exercising caution before opening unknown files and not downloading content from untrusted sources to avoid this type of issue."
Proofpoint also urged Microsoft Word users to install the security updates quickly.
"Because of the widespread effectiveness and rapid weaponisation of this exploit, it is critical that users and organisations apply the patch as soon as it becomes available," the firm said.