I would hope that most of you have learned this lesson by now, but for those who came in late: there is currently no Wrath of the Lich King beta test going on. We've been getting a steady stream of tips about various scam sites, or questions along the lines of "is this invite I just got real?" No, that beta invite you got from "firstname.lastname@example.org" is not real. Wrath is in alpha, company-internally, maybe. Trust me, I want in at least as bad as you do, but any invite you get to a Wrath beta right now, unless you work at Blizzard, is fake.
When the beta does start (as it surely will eventually), and if you're lucky enough to get a real invite, it will point to a site at blizzard.com, worldofwarcraft.com, or (for our European chums) wow-europe.com. It will not, for instance, point to therealblizzard.net. The scammers have gotten pretty good at building convincing-looking sites (as pictured), but check the URL and don't be fooled. Do not enter your WoW account name and/or password anywhere other than the log-in screen of the game, blizzard.com, worldofwarcraft.com, or wow-europe.com. Oh, and use Firefox.