Is Open Source software really more secure?

[Bud Rogers <budr@sirinet.net>]

I've always taken for granted the idea that open source was inherently more 
secure because it's open to peer review.  Linus said "Given enough eyes, all 
bugs are shallow."  But has anyone ever done a serious study on the subject?  
 I've seen plenty of emotional arguments and anecdotal evidence, but nothing 
that I would consider hard evidence.  

I'm doing a paper on this topic for a graduate level class in Information 
Assurance Management.  I'm looking for background material for my paper.  I 
would appreciate any pointers, urls, etc.

-- 
Bud Rogers <budr@sirinet.net>