Md5sum

MD5sum is a way of checking that a file is exactly the same as it was when it was first made. It works by creating a special "code" (called a "hash") from the contents of the file. Any time you open the file, you can check the MD5sum code to make sure it hasn't changed. It is like a fingerprint of the file that you can use to make sure it is safe and hasn't been changed.