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BD+ Technologies has distributed the finished version of the copy protection system to studios, with Fox likely to be the first to implement a technology that it has backed from the beginning.

Following a breach of the AACS copy protection that Blu-ray shares with HD DVD, the Blu-ray Disc Association announced in April that it had brought forward the planned release date for BD+. Unlike AACS, which applies the same encryption key to all copies of a movie, BD+ allows each disc to install

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a small piece of encryption software on a player each time a disc is inserted.

This virtual machine, which is deleted when the disc is ejected, can perform three tasks. It includes transform code that unscrambles sections of video on the disc that would otherwise be corrupted; it can check whether a player has been hacked by looking at changes to the firmware version, for example, and disable playback on that specific player; and it can run additional code at the same time as the disc is playing that may be used to provide an additional, custom layer of protection.

It is this third component that is most open to abuse, since it begs the question: what might studios do with the additional powers that BD+ provides them? Discs that expire after a certain date are among the possibilities.

But following Blockbuster's vote for Blu-ray, the introduction of BD+ tips the balance even further in the format's favour, since it's likely to encourage studios to release even more titles on what will be a more secure platform than the rival HD DVD. At least, until someone manages to reverse engineer the virtual machine.