If you really want to do hands-on, information-security work, I'd strongly recommend the MS in security, because it's a more technically-focused degree (which I assume would be either in computer science or engineering). I'd also urge you to pursue the Certified Information Systems Security Professional (CISSP) certification (http://www.isc2.org) and the CPP (Certified Protection Professional); for more info on the CPP, visit http://www.asisonline.org.
Based on your current degree and experience, you sound like you're already off to an excellent start!
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This was first published in April 2003