Here is a step by step tutorial to get rid of this message:
Step 1: Click Start>Run and type
gpedit.msc. Click OK.
Step 2: Go to
User ConfigurationAdministrative Templates Windows Components
Attachment Manager.
Double-Click on "
Inclusion list for moderate risk file types" setting and click apply.
Step 3: Add "
*.exe" to the "
Inclusion list for moderate risk file types" setting. You can also add other file types.
This should disable the "Publisher Could Not Be Verified" messages from appearing for that file type in the future.