Looking at my email today, I found about a hundred zip files. All of them were spam, and I'm guessing that all of them were malicious software - trojans.
My guess is that the trojans were sent as zip files because for some systems, if you click on the attachment, then the computer unzips it, finds an executable inside, and runs it.
I don't know which trojans are being sent - I'd guess they are a few different ones because the file sizes are different. But what impressed me today, was the volume.
100 trojans sent to me per day! The zombie apocalypse is here.
My email system sorts my email; emails with attachements that are zip files (or similar) go into their own area. And then when I look there, I delete them.