ESRI has issued a warning that a particular set of patches called a “hotfix rollup” for Windows 7 and Server 2008 will cause problems with ArcGIS. Do not manually install “hotfix rollup” KB 2775511.
This rollup is not part of the normal suite of patches delivered to Windows computers, and regular updates from MicroSoft do not pose a problem. A user would have to manually download this hotfix package to install it.
There are reports that this MicroSoft patch may have caused problems with other software as well – for example, here. (See last comment.)
When a patch is available for ArcGIS, this blog article will be updated. Patches for ArcGIS are available at the download site.