http://www.newsforge.com/article.pl?sid=03/11/06/1532223

for a blow-by-blow report
http://kerneltrap.org/node/view/1584

Basically some university computer was used to try to stick a 
back door into the 2.6 kernel. Due to the excellent structure
of the kernel development tree, this did not happen. One of
the reasons why open source is a better development choice
than closed source. Maybe. ;)