
As for BT. There may be a way to prevent leechers from hopping onto a Torrent and leeching the stream w/o giving anything back. The fact that it's open source only leads to this being more of a possibility. But if they did implement peer-tracking in the tracker, they would want to ask other peers about a certain peer instead of asking that peer directly, since the peer could probably just spoof its upload rate.
BT was written in Python and comparing it to dos is o_O. Dos was a OS, it's far bigger and far more complex and there were viruses and exploits for DOS back in the day. However people did that even with out the source to DOS.
~klinky