How can AnyDVD destroy a DVD drive?

I have done exactly this a few times and it has never broken the drive. Effectively running the player software supplies the drive the decryption key for the disk which VLC then takes advantage of.

At worst playing a region 1 disk on a region 2 drive will set that drive to region 1. Most commercial drives can only have their region changed 5 times before they "lock" to that region.

It may well be that your friend "locked" their drive to region 1, preventing them from playing region 2 disks rather than it destroying the drive.

Software that ignores the drive region and performs the decryption themselves would not be affected but commercial players would no longer work, except with region 1 disks.

Some drives can be flashed with region-free firmwares that never lock.

I have no idea what AnyDVD actually does, but I can speculate. Here are some scenarios that could lead to this:

• It could be that AnyDVD recognizes a bunch of drives intimately and performs manipulations with their firmware, or at least employs some non-standard undocumented low-level commands. It enables its special mode when started, and returns the drive to "vanilla" state when exiting. Except that this time, due to VLC or some other unfortunate coincidences, the shutdown process didn't succeed, and instead left the drive in a messed up state.
  • As a special case of this, as noted in other answers, perhaps the drive wasn't even bricked - it was just locked to the wrong region and refused to change that. Thus disks with other regions didn't work. This could be tested by trying to read a region-free disk or a data disk.
• The Wikipedia page states that AnyDVD is a driver. Which makes sense - it's a good place to intercept of drive access at a low level. It could be then, that AnyDVD didn't actually mess up the drive - it messed up itself. The drive was fine, but AnyDVD's driver wasn't. As a result, the drive couldn't be used anymore - on that computer. This could be easily tested by putting the drive in another computer or reinstalling Windows from scratch.
  • As a special case of this, perhaps it also alters other drivers in the system "on the fly". Like changing the code in them. This is, of course, very difficult and risky, since any change to the other driver (can happen at any time with a Windows Update) would mean that AnyDVD's patches are useless or worse - harmful. I don't expect that they actually did this, but it is a theoretical possibility.