As part of its regular Patch Tuesday, Microsoft released an update for its various toolbars, and this update came with more than just documented fixes. The update also installs an add-on for Internet Explorer and an extension for Mozilla Firefox, both without the user's permission. As you can see in the Windows Update screenshot above, Microsoft does not indicate that the update will install anything for either browser. It's also not really clear what the installed extension actually does.
To make matters worse, the update was marked "Important" instead of "Optional," which means it was more likely to be installed either automatically (if the user has Automatic Updates on) or manually when the user clicks Install (Important updates are checked by default).
The Microsoft Support page for this update,
KB982217, describes the issues the update supposedly fixes: "In an Internet browser, you specify a homepage that is not a fully qualified URL. However, Windows Live Toolbar, MSN Toolbar, or Bing Bar may not categorize your homepage correctly. Therefore, the homepage reporting may be generated incorrectly for users who select the Help improve our services option when they install these toolbars."
The Bing Bar, which has replaced both the Windows Live Toolbar and the MSN toolbar, is available for both Internet Explorer and Firefox, which is why we assume that only these two browsers are tampered with. Still, the KB article does not mention an add-on or an extension being installed or updated.
Since we could not find any official documentation from Microsoft, we checked the actual IE add-on and Firefox extension. Unfortunately, they were not terribly helpful; all we discovered was that the IE add-on is at version 3.0.126.0, so it has been around for a while, and that the Firefox extension is at version 1.0, so it's likely it was only released now. Both seem to be installed in "C:\Program Files\Microsoft\Search Enhancement Pack\Search Helper\." Inside, there is a file called "SEPsearchhelperie.dll" that is responsible for the IE add-on and a "firefoxextension" folder responsible for Firefox. The update can't be uninstalled, but deleting these files works just fine.