The free DiamondCS MD5 utility doesn't compute correct md5 hashes for very large files. I've tested with the latest Knoppix cd (696MB): KNOPPIX_V5.0.1CD-2006-06-01-EN.iso which official md5 is 653acc801d4059598bd388de8171a20d. This value is properly given by md5summer and hashcalc for example. But DCS MD5 gives 4CAEF60394D90C68A6F0548B52C33351. However, proper md5 values are given for smaller files, at least up to ~100MB. I've not tested where DCS MD5 breaks down.