Recent reports suggests that the BitTorrent DNA, which is bundled with the mainline client, is an “exploitable” version of uTorrent without the user interface. It is suggested that it is possible for any websites to offload content to the btdna.exe, without the user’s consent!!!
BitTorrent DNA is used for p2p streaming of online videos. It works like this; the user who wants to watch a stream has to install the BitTorrent DNA application, which is also bundled with the BitTorrent mainline client.

When the user plays a BitTorrent accelerated stream it will not only download data, but also upload it to other people who are watching the same stream, similar to a regular BitTorrent download. (more at: torrentfreak.com)