Hash fails and wasted data. whats that mean?

[grouchpunk08]

I have been using utorrent and downloading torrents for a year or two now, but I have always wondered what it means when it says, for example: Wasted: 17.9MB(3 hashfails). Most of the time i dont have any wasted data, but do have hasfails, and even when I do have wasted data, the torrent is completely intact when I finish it. Any want to explain what that whole wasted data and hashfail thing is about? I've always wondered. Thanks in advance

[Switeck]

The documentation covers that nicely.