md5sum passes then fails later

[milton1]

Hi all, I have a strange one here:

Downloaded kubuntu alternate x64 iso, md5sum passes.
Downloaded kubuntu alternate i386 iso, md5sum fails.
Downloaded ubuntu alternate i386 iso, md5sum fails.
Re-check kubuntu x64 iso, md5sum fails!
What happened? I did nothing to the file; no moving, no renaming, no attempts to burn, nothing! Why is the md5sum now failing? I now do not know if the iso's I have downloaded are good or not. Please, any advice will be helpful.

[milton1]

If it helps, md5sum is giving the same (incorrect) result every time I use it now on a given file.

[milton1]

Update: copied the iso's to a new computer, tried md5sum again, failed. So it seems that the file somehow corrupted. I downloaded these via bittorrent; could something have gone wrong in the switch from downloading to seeding?