A checksum or hash sum's a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and comparing it with the stored one. If the checksums don't match, the data was certainly altered. The procedure that yields the checksum from the data's called a checksum function or checksum algorithm. A… (More on Checksum)