One of the most common uses is to make sure that a file that you have downloaded is not corrupt. Some websites post the MD5 checksum of a file on their download page. Once you have downloaded the file, use winMd5Sum to get the MD5 checksum of the file on your computer. Then make sure that the MD5 checksum from the web site is the same. If they are the same, then your file is exactly the same as the file on the website.