Microsoft today released nine update bundles to plug at least 55 distinct security vulnerabilities in its Windows operating system and other software. Three of the patches fix bugs in Windows that Microsoft considers “critical,” meaning they can be exploited remotely to compromise vulnerable systems with little or no help from users, save for perhaps clicking a link or visiting a hostile Web site.

The bulk of the flaws (41) addressed in this update apply to Internet Explorer, the default browser on Windows. This patch should obviously be a priority for any organizations that rely on IE. Other patches fix bugs in the Windows OS itself and in various versions of Microsoft Office. A full breakdown of the patches is available here.

Among the more interesting critical patches is a fix for a vulnerability in Microsoft Group Policy that could present unique threats for enterprises that rely on Active Directory, the default authentication mechanism on corporate Windows networks. The vulnerability is remotely exploitable and can be used to grant attackers administrator-level privileges on the targeted machine or device – that means 10s of millions of PCS, kiosks and other devices, if left untreated.

Several readers who’ve already applied these updates report that doing so may require multiple restarts of Windows. Patches are available via Windows Update, the patching mechanism built into all recent and supported versions of Windows. For more granular information about these patches, check out this blog post by Qualys as well as the always-useful roundup at the SANS Internet Storm Center.

As always, if you experience any issues applying these patches or after applying them, please leave a note in the comments section below describing your experience.

Tags: February 2015 Patch Tuesday, internet explorer, Microsoft Active Directory, Microsoft Windows