Microsoft is issuing a security update to fix a record 64 vulnerabilities, including a months-old MHTML flaw.
Of the 17 patches, nine are rated critical and eight are important, according to Microsoft. They cover flaws in Windows, Office, Internet Explorer, Visual Studio and more.
The update addresses a MHTML flaw uncovered in January. Google said last month that the vulnerability was being used in "politically motivated" attacks against its users.
"This is a huge update and system administrators should plan for deployment as all Windows systems including Server 2008 and Windows 7 are affected by critical bulletins," advised Amol Sarwate, manager of the vulnerability research lab for security firm Qualys.
"Frequently used office applications like Excel 2003 through 2010 and PowerPoint 2002 through 2010 are also affected."
Paul Voss, senior response communications manager with Microsoft, said the software giant would also shut down several security alerts, including a critical one in Server Message Block Browser.
"Microsoft assessed the situation and reported that although the vulnerability could theoretically allow Remote Code Execution, that was extremely unlikely," Voss said in a post on the Microsoft security blog.
"To this day, we have seen no evidence of attacks."