Is Linux as Secure as We'd Like to Think?

man_of_mr_e asks: "With all the recent brouhaha about Blaster and Sobig, there's been a lot of talk about how poor Windows security is, especially compared to the Linux we all know and love. But is this really true? The website defacement archive at Zone-h shows that Linux accounts for 61% of the defacements in the last 24 hours (note, this figure changes, so it might be different when you view it). An analysis of the last few weeks of their archive shows a similar percentage of exploited Linux systems. Note also that the 'Unknown' category is rather high, and certainly contains at least some Linux systems, further increasing the percentage. Why is this? Are we just deluding ourselves about our own security? Could there be a Linux 'Blaster' just waiting to happen?" While "defacements" don't necessarily mean "root level break-in", sometimes getting your foot in the door is enough. If this happens, wouldn't Linux then be just as exploitable as Windows? Are there other reasons why the likelihood of a "Sobig" or an "ILUVYOU" would be lower for Linux than Windows?