A worm unleashed in the summer of 1999 that infected Microsoft Exchange mail servers. It replied to each incoming message with "Hi <sender name>! I received your email and will send you a reply ASAP. Till then, take a look at the attached zipped DOCs. Bye." When the attachment was double clicked, it deposited an executable file in the Windows folder that proceeded to delete the data in Microsoft Word, Excel and PowerPoint files, as well as assembly, C and C++ source files. It also spread to every machine in the network.
These are Microsoft Office files after the Worm.ExploreZip virus was unleashed in the local network. When you find your files have 0 bytes, you truly understand what backup in a remote location means (see off-site backup