Just because I was curious, I did some checking on my site here. I have 1,454 posts here on Terminal23.net dating back to 8/9/2004. That’s 19 posts per month. Prior to that, I made all my posts on my personal blog at HoldInfinity.com (less geek, more personal blog), which has 268 posts since 10/05/2001. I’d say I’ve been blogging about security since 2004.
Even prior to that, I’ve had a web site since 1997 (maybe late 1996 if I really push the definition), but are no longer available except maybe on a floppy somewhere in a desk.