This is what our IT guru emailed us this morning... sounded relevant.
The recent 'Bagle' worm launched earlier this week, and we would like to provide you with best practice information on how to protect yourselves (and the rest of us!)
The worms attempt to avoid detection by arriving as a password-protected ZIP files; as a result, virus scanning services cannot detect the viruses contained inside. The password is contained in the body of the infected e-mail, so the user can choose to manually decrypt the ZIP file if they wish.
E-mail characteristics include a spoofed "From:" address, random phrases in the subject field, and no message text.
So, unless you're expecting an encrypted or password protected .zip file, don't open one.