MS Proxy 2.0 – Firewall?

I’ve been using MS Proxy 2.0 as a firewall/proxy server for years, I’m convinced it’s secure. I’m no hardened hacker by any means, but I feel that Proxy 2.0 — although, using the default settings leaves you wide open like Madonna’s knees — is sufficient to use as defense from internet hackers. Alot of people disagree,(especially, it seems, everyone who talks to my boss 🙂 do you? 500 points each to the most helpful answers . . .