There's a new security patch for Windows that's undocumented but appears to fix a known problem with one of last week's Black Tuesday patches. It isn't clear at this point if the re-issued KB 3013455 solves the problem all by itself, or if it has to be augmented by the undocumented KB 3037639.

One of the February Black Tuesday patches, MS15-010/KB 3013455, had an acknowledged side effect. Although the patch was (yet another) Windows kernel mode driver update, the KB article stated that:

After you install security update 3013455, you may notice some text quality degradation in certain scenarios. The problem occurs on computers that are running the following operating systems: Windows Server 2008 SP2

Windows Server 2003 SP2

Windows Vista SP2 Microsoft is researching this problem and will post more information in this article when the information becomes available.

There's a lengthy thread on the Microsoft Answers forum that details the problem. Particularly for Vista and Windows Server 2008 users, and apparently for XP users, the "text quality degradation" can make it very difficult to read text in Courier and other simple fonts in Windows system programs, browsers, and other apps. Programmers -- who tend to work in environments with simple fonts -- were particularly vocal. Suggested workarounds included changing fonts where possible.

Uninstalling KB 3013455 solved the problem, but doing so left systems exposed to the patched kernel-mode driver vulnerability.

Although the problem was obvious and replicable, and acknowledged in the KB article, Microsoft didn't pull the update.

Apparently on Tuesday, February 17, Microsoft released a fix for the problem in the form of a new patch called KB 3037639. As of this afternoon, there's no documentation for the fix -- in particular there's no KB article 3037639. All we know for sure is that installing KB 3037639 on top of KB 3013455, or in place of KB 3013455, cures the font funnies.

Poster ShawnDream hit upon the fix:

The link for all downloads is: http://www.microsoft.com/en-us/search/Results.aspx?q=kb3013455&form=DLC Choose your OS from the half dozen big options at the top and it brings you right to the download page. Hit the big red download button and it should offer you two updates: kb3013455 (the original that breaks fonts) and KB3037639 (the secondary update to fix fonts) I installed the original, said do not reboot, and installed the second. After reboot I appear patched and my fonts are good.

If you go to the Microsoft Download Center, you can see that the KB 3013455 download on offer has a new publication date, Feb 17.

The KB 3013455 article hasn't been updated. It still shows that it was last reviewed on Feb 12.