How to disable irritating Office File Validation security alert?

Looks like they increased security toward their old file formats in order to avoid vulnerabilities.

Here is some information on why it does this and how to convert the files so you won't get the error message.

Two updated error messages for the Office File Validation feature in Office 2007 SP3 now provide more detailed information and options. You will encounter these messages if you attempt to open files that are stored in Office binary file formats and if the files do not pass scanning and validation checks. Note: Office binary file formats are also known as Microsoft Office 97-2003 file formats.

...you can click the safer options link and then use one of the following options:

1. View the file in Office 2010 by using Protected View
2. Use the Microsoft Office Isolated Conversion Environment (MOICE) feature
3. Open the file inside a virtual machine

Found some possible workarounds at Microsoft Technet which might be helpful. About half way down the page are some options to control how it works.

To prevent Office File Validation from validating files you must create the following registry keys & values, and assign a DWORD value of “0” for the specified application in Office 2003 or Office 2007:

Keys:

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\<version ie 11.0 or 12.0>\<app eg Word or Excel>\Security\FileValidation

Values:

(all) EnableOnLoad DWORD 0  
(Excel) PivotOptions DWORD 0  

As an example, to disable file validation for Word 2007 you need to:

add value

EnableOnLoad DWORD 0 

to key

HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\12.0\Word\Security\FileValidation

Close any Excel window (If open), and then perform the following steps:

1. Click Start, click Run, type regedit, and then click OK.
2. Locate the following registry key: HKEY_CURRENT_USER\Software\Microsoft\Office\11.0 or 12.0\
3. Click on the version number to highlight it On the menu, click Edit, New and then click Key. Type Excel, and then press ENTER.
4. Select Excel, point to New on the Edit menu, and then click Key. Type Security, and then press ENTER.
5. Select Security, point to New on the Edit menu, and then click Key. Type FileValidation (Note there are no spaces between the words), and then press ENTER.
6. Select FileValidation, point to New on the Edit menu, and then click DWORD (32-bit) Value. Type EnableOnLoad (With no spaces), and then press ENTER.