This error will be occurring due to the Internet Options settings in your Windows operating system. See the steps below to top the message from appearing.
Note: if you are not able to see all the options in the steps below, you may have to get your IT Network administrator to perform the steps.
Click on the Start Icon in the Windows task bar.
Type Internet Options.
Launch the Internet Options app.
Select the Security tab.
Select the Custom Level button under the Internet section.
find the option Launching applications and unsafe files.
Select Enable, and then click OK to save the change.
Close the Internet Options window, and re-open Attaché. The file security warning message should no longer appear.