A competing store marketed their DRMed music as being iPod compatible, and then when Apple found out that their DRM had been broken / stolen (whichever the case may be), they changed their algorithm via an update. The update thereby meant that the competitors songs that were purchased and loaded through a violation of Apple's intellectual property per their cryptographic algorithms and signing certificates were no longer capable of being used on an iPod as they did not validate as being a *true* purchase, per their legal requirements to limit usage to a single user under their license agreements to sell songs to end users digitally.
As a car analogy, let's say that Ford sells you a Focus.
Aftermarket reseller WYSIWYG, LTD. then buys a Focus and figures out how particular tools are made, writes manuals, and then starts making their own aftermarket parts for everything. The problem is that WYSIWYG's one they got had a manufacturing defect... It's drive shaft was incorrectly cast and would crack at high speeds, and the tachometer was mis-calibrated.
They don't know so they just make more identically to the first, and sell them on to their customers. Ford fixes the issue in their manufacturing, issues a recall, and while they are at it slightly alters the housing.
Competing school of though as a car analogy, let's say that Ford sells you a Focus.
Aftermarket reseller WYSIWYG, LTD. then buys a Focus and figures out how particular tools are made, writes manuals, and then starts making their own aftermarket parts for everything. One day they get the idea, we have every single one of these parts sitting on our shelves, why don't we just start selling our own Focuses? We can even call them Ford Focuses, by WYSIWYG and do it at a discount because why not.
Ford tells them to stop, WYSIWYG ignores them, Ford just changes their assembly line, making WYSIWYG's legacy parts no longer useful.
The problem. Here is that car analogies really do not translate into IP issues.