I've seen zip files being used when the file extension of the file is considered suspicious. I know that it would be simple for them to rename it and send it that way, I suspect that the majority of users haven't even turned "hide extension for known files" off. Where as double clicking on a zip file is a common thing for users to do. I'm not impressed with zip, as the other day I downloaded a development framework in a zip, moved it into position and then wondered why my compiler was still saying it couldn't find the headers, it took me a while but I eventually discovered that none of the symbolic links were symbolic links, they were a file with the text of the location.