Depending on your current background and knowledge base, you could start with a variety of entry points:
1. Start easiest with the BrainBench credentials.
2. Tackle an entry-level cert to begin with (this may work best for you, unless your academic and conceptual background is very strong). For this position I'm currently recommending the CompTIA Security+ exam, which goes live in late October or some time in November (a bargain beta is available through Monday, Sept. 30, for half price).
3. Jump into an intermediate level cert like the CISSP, CISM (a brand-new credential from ISACA, the Certified Information Security Manager) or mid-range SANS GIAC certs).
Since I don't know what you've been doing for the last six years, or about the strength and generality of your security background, I can only suggest you investigate all three options and choose whichever one works best for you.
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This was first published in September 2002