Md5sum allows you to verify that downloaded Shorten (.shn) files are not corrupted or otherwise unusable before you burn them to disc or host them on your file server. Do this by checking these files against an .md5 file. An .md5 is a simple text file that contains a 'fingerprint' of each Shorten file. When you perform an md5 check, you are comparing the fingerprint from the files you downloaded to the fingerprint of the files on the server you downloaded from. If the md5's (fingerprints) match, you have an uncorrupted Shorten file.