After installing MS12-030 (http://support.microsoft.com/KB/2597166 for Excel 2010 or http://support.microsoft.com/kb/2597162 for Excel 2007) you may notice a problem with files that contain links to other spreadsheets.
This problem won't happen to all users and may not affect all of the links in the spreadsheet, but some of the links may be affected the following way:
Spreadsheet 1 is located in Folder 1 and contains a UNC link to Spreadsheet 2 which is located in folder 2. After applying this security update you may find that Spreadsheet 1 now links to the same file, but in Folder 1 where it doesn't exist.
This problem only affects UNC links and only affects the new Office file format - in other words XLSX, XLSM, etc. The legacy XLS file format is not affected.
The following fix will resolve this problem. You must apply the August 2012 cumulative update and recreate the links.