I do not need a solution (just sharing information)
The information in this blog post from Security Response will be of interest to mail admins:
.Zip Attachment Spam Makes a Grand Return
https://www-secure.symantec.com/connect/blogs/zip-attachment-spam-makes-grand-return
Trojan.Zbot and Trojan.Cryptolocker have been spreading through infected attachments. Definitely ensure that your organization's mail security software is working correctly!