The ISS X-Force team (they look like an outtake from a, Seattle’s own, MotherLoveBone video back in the day) has been compiling stats on vulnerabilities. In 2005 the compiled a list of 4,472. What they have noticed is the ever growing number of so called zero day exploits. These are ones that are released on an unsuspecting interweb without so much as an advisory.
“The rapid development of exploit code following public disclosure will inevitably lead to increasing infection rates of bot-worms and malware such as spyware and rootkit installer agents.”