but a commercial program DVD can no longer be read by any drive.
...
This didn't just happen once, but keeps happening to one specific DVD.
Now, to recap, then, and for clarity sake. This is a pressed commercial DVD, not a DVD+/-R/RW? And the same disk has failed multiple times? (ie, you purchased it, it failed, you exchanged it, the new one failed, etc..?)
If that's the case, I'd say it was probably a bad production run for the pressed disk. Or something you're repeatedly doing to that particular disk. Does it sit in the sunlight? Does it get stored differently from your other disks?
If you're talking about a DVD you're burning that works for a little while and then fails, I'd likely blame the burner, or the disk brand you burned it on, in addition to the sunlight and storage questions.
I suspect something is being reprogrammed in the computer/DVD by some one who has invaded my systems here.
Personally, I'd think that even more unlikely than a non-physically-tampered-with DVD reader accidentally "writing" something on a DVD. And I'd rate the odds of a DVD reader altering a DVD in a way that doesn't involve physical scratches, cracks, or warping, at about the same odds as winning the lottery jackpot.
Look for the simple explanations. They're usually right. The problem is sometimes they're so obvious they're hard to see.