A changing landscape
In 2004, I came across an empirical study published by the CERT/CC that indicated a diminishing correlation between the number of vendor-issued vulnerabilities and the number of reported security incidents. In the years prior to 2002, the number of reported security breaches had always been proportional to the number of vendor-published vulnerabilities. That corollary made sense, since attacks and worms followed vulnerabilities. However, in 2003 and beyond this was no longer the case. The number of incidents rose dramatically as compared to the number of published vulnerabilities.