Enabling BitTorrent Encryption
From SDA Knowledge Base
If you are experiencing slow or nonexistent downloads or uploads using BitTorrent, enabling encryption in your BitTorrent client may help.
µTorrent
µTorrent is a popular BitTorrent client for Windows. Enabling encryption in it is easy.
First, choose Preferences from the File menu:
Then click BitTorrent at the left, then choose Forced from the Protocol Encryption: Outgoing dropdown menu:
Then click OK.
Although you may also simply choose Enabled to let µTorrent choose when to use encryption, if your ISP is using so-called "traffic shaping" to slow down your BitTorrent traffic, this may not be as effective as choosing Forced.