The 3 beta test is expected to launch today, and if you're entering the eagerly-anticipated preview via most methods you'll be able to begin downloading the trial now. If, however, you're one of the people attempting to enter the beta via the special invite, then there's a problem. It doesn't seem to be working yet.

For their part, developers assure us they are aware of the problem and are working hard to get Crackdown users (probably the largest beta contingent) into the game. "With any luck this will be a short delay. People entering the through other methods - Friends and Family, Rule of Three and so on, are unaffected," read a quick post on the official Bungie site earlier.

The 951MB beta download was scheduled to be available from 1pm GMT today (unless you're a Crackdown-participant, it would seem), and gives you access to three maps. Feedback from these three levels will be used by the developers to improve the final product. You'll need not only some form of entry key, but a Live Gold account and sufficient hard disk space, too. The beta is scheduled to finish on June 7th at 7.59am GMT.

Update 2: And we're - almost - back. All the problems with Crackdown users' entry into the beta appear to have been resolved and downloads can now progress once a new Crackdown patch has been installed. Bungie and have apologised for the and duly extended the beta period until June 10th at 11.59pm PDT. Four more days. Not bad at all...

We'll bring you all the latest Halo 3 beta news as we get it.

By Luke Guttridge