BitTorrent.com's BitTorrent client installs a browser toolbar in Google Chrome, Internet Explorer & Mozilla Firefox.

There isn't an opt-out option to stop the toolbar installation when installing Bittorrent so you need to uninstall the toolbars after installation.

To Uninstall:

Google Chrome:
Goto Wrench ==> Options ==> Extensions
or
enter chrome://settings/extensions in the location bar

click Remove next to the Bittorrent Toolbar

Mozilla Firefox:
Goto Firefox ==> Extensions
or
Press CTRL+SHIFT+A
or
Enter about:addons in location bar

Then click Remove

Internet Explorer:
Go to Control Panel ==> Programs and Features and right click on the "BitTorrent Toolbar" entry (not BitTorrent) and choose uninstall

Versions:
BitTorrent 7.6 (Build 26764)
Windows 7 Ultimate 64bit