An article by Professor Spafford on the relative security of open source software has been published by G4Tv.com
From the article:
We often hear debate about which is more secure: open source or proprietary source. Each side makes arguments and refutes the arguments of others. In truth, neither is correct (or both are). Whether or not source is proprietary does not determine if the software is better. Instead, other factors are more important in determining the overall quality and trustworthiness of a system.