All downloadable products from Tapspace are delivered electronically via the internet using the .ZIP file format. Some antivirus software re-names files with .EFW when downloading. This can sometimes happen if you are using Internet Explorer and click on the download line and choose run instead of save. Try using the save option, and save it to a location that you can find easily (like your desktop), then you should get the proper .zip file extension.
If you save the file and notice that it's still given the .ewf extension, simply rename the file to .zip rather than .ewf.