https://help.ubuntu.com/community/TOR
sudo /etc/init.d/tor stop
Security issues with Tor
exit nodes can sniff traffic. Information about who is making the connection can be gleaned from plaintext information
a single entity with a sufficient number of nodes could be both an entry and exit node for a random user. Although traffic to/from the "target" user is encrypted by the user, the intermediate and exit nodes are both controlled by the same entity. Thus the entity would be able to know all the traffic of the user
This would not apply if the user were browsing to tor-only sites (with onion addresses)
http://hal.inria.fr/inria-00574178/en/
https://addons.mozilla.org/en-US/firefox/addon/betterprivacy/
Portable Tor browser (web only)
http://en.wikipedia.org/wiki/Portable_Tor
http://en.wikipedia.org/wiki/Torpark
Rather than run TOR on an everyday personal or work computer (Windows or Mac or Linux) with sensitive data and identifiable traits, I'd recommend booting a LiveCD: TAILS (v0.7.1 is the latest) and Liberté Linux:
or get Knoppix and harden it
Change your MAC and connect at a coffee shop (if paranoid, on the other side of town, and wear sunglasses in case of surveillance), not from home. Or connect to someone else's open WiFi, or get the key with Backtrack. Less secure is running a LiveCD in a VM (virtualbox or vmware). Another less secure option is running a hardened Linux, or at least running the Bastille script.