Email viruses propgate by tricking the recipient to execute a virus-laden attachment. Some email applications may automatically open or execute an infected file. To make it less likely that recipients will accidentally execute a malicious attachment, the ACCC runs all incoming email through MIMEdefang, a service that automatically renames files of certain types in order to prevent automatic execution. MIMEdefang adds a .txt extension. To restore the file, simply rename the file and remove the .txt extension:
Important note: Microsoft Word and Excel files are not MIMEdefanged. These files can carry macro viruses. It's important to remember that files from people you know and trust can also be infected with viruses, so it's vital to use anti-virus software (whether your computer uses Windows or Mac OS X) and keep it up to date with the latest virus definitions.
List of file extensions which will be renamed by MIMEdefang (popular extensions highlighted in bold):
August 18, 2012