The covert threat.

As well as many other PC users, I from time to time copy the files which have collected at my hard disk to compact discs. And as CD-writing drive at our office only one, I am due to copy these files over a local area network to the computer with this drive.

Having done once again this operation, I have found out, that the ZIP-file written down on a compact disc can not be unpacked. It has slightly surprise for me, since neither at copying, nor at recording, at the subsequent reading I did not receive any error messages. More detailed investigation has revealed, that the file was damaged at copying over network. Fortunately, I had not time to remove an initial file, and simply anew have copied a file.

After that case I have decided, that it is necessary to find means for the control of integrity of copied files. After short searches I have found the md5sum utility. This utility calculates the checksum of the specified files by MD5 algorithm. By comparing the checksums of a file before and after copying, I can check up identity of an initial file and a copy. It was all that is necessary for me!

Having begun to use this utility I have found out, that each time when I copy files to CD - R, usually several files has been found damaged. These damages occurs both at a stage of copying over a network, and at recording on CD - R. I do not know, why it occurs: because of bad quality of the equipment, or because of the software bugs. Or, maybe, the error correction algorithms incorporated in them begin to give failures at such volumes of the information. At least, now I had means of detection of the latent damages and I was once again convinced, that extra check never will superfluous…