easy_install in setuptools before 0.7 uses HTTP to retrieve packages from the PyPI repository, and does not perform integrity checks on package contents, which allows man-in-the-middle attackers to execute arbitrary code via a crafted response to the default use of the product.
https://pypi.python.org/pypi/setuptools/0.9.8#changes
http://www.reddit.com/r/Python/comments/17rfh7/warning_dont_use_pip_in_an_untrusted_network_a/