A quick Google search for the .ewf file format shows that it's a compressed .exe or .zip file type. I don't quite understand why the mod would be in ".ewf" format, but according to the web site it may be attributed to your anti-virus software.
To fix it, simply right click on the file, and change the extention at the end from ".ewf" to ".exe". Once you've done that, you should be able to open it.
Good luck
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