Microsoft will this week issue nine security bulletins to fix 21 vulnerabilities, with four labelled "critical" and the rest "important".
The company on Thursday said the critical fixes would address flaws that could allow remote code execution in Windows, Internet Explorer, .NET Framework, and Silverlight, Microsoft's web development tool.
"Important" patches would address bugs in the Office suite, as well as server software, that could allow privilege escalation attackers to access more than intended through privilege escalation.
Wolfgang Kandek, CTO at vulnerability management firm Qualys, said the critical update to Internet Explorer should receive the highest priority, as criminals were ramping up their use of browser-based attacks.
"A couple of years ago, email was the most prevalent method of attack," Kandek said.
"Today, it is web browsers."
To illustrate his point, Kandek highlighted a vulnerability that was patched 10 January by Microsoft but was exploited roughly two weeks later.
The attack was delivered through the browser and involved a malicious audio file played via the Windows Media Player.
As usual, Microsoft advised users to apply these patches via Microsoft Update, Windows Update and the Microsoft Download Center to keep their software up to date.
Mac users can receive uploads automatically with Microsoft AutoUpdate for Mac.
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