They wouldn't really have to leave a trap. They could just build a database of hash values of the files already available there.

Yes, but when that MP3 is bit-for-bit identical to the version of the song that was downloaded millions of times from bittoreent (or gnutella etc.) you are going to have a tough time arguing that you got it from some other source.

Because their strategy has been to go after the big fish, people with large numbers of files hosted. But now, if they have access to a centralized database of what music files people have on their computer it becomes low hanging legal fruit.

The argument will be made that the leecher made one unauthorized copy of the song...the copy that came from the file sharing service to their computer's disk. It may be just one little copy but it was clearly the leecher's intentional action that created it. Copyright infringement is in the copying.

Well I guess in either way it is a laundering service. The real issue is in what way. The optimists think that Apple will launder all of the dirty laundry for $24.99. The article thinks that you will store all your laundry for $24.99 and then the RIAA laundry inspectors will accuse you of having hundreds or thousands of dirty shirts. And then Apple will allow you to clean that laundry and get rid of the laundry inspectors for just 99 cents a song!

Well, presuming that your CDs never went up to or down from a file sharing service then their signatures are most likely unique and would not raise suspicions. But also bear in mind that Apple's 'minutes, not weeks' statement would not apply to your collection.

Lala was small potatoes, I believe that Amazon de-dupes files purchased through Amazon (which are undeniably legal) but other files are just stored. Google also does just storage. The difference is with Music Mach is Apple is keeping a big central database of who has what.

You realize of course that if Apple banned all RIAA member publishers then iTumes would be essentially empty?

Everybody knows that the tech behind iCloud came from LALA, So?

A poor choice of phrase.

I am not an RIAA lawyer but I suspect that their argument will go like this: In order for iTunes Music Match to find the song it had to be on your disk. In order for it to be on your disk you made a copy of the song without the rights to do so. The act of making that copy was a violation of copyright. You had 10,000 such files. But then out of the shadows steps your hero Steve Jobs! He offers that with one click you can make all ten thousand copies legal and make the RIAA go away! And it will only cost you $9,900!

What the RIAA would argue is that the act of downloading the file was making a copy. It was taking the song that was on the file sharing system and making a copy on your disk. In other words the existence of the file isn't the problem, it is the act that created the file.

Exactly, It isn't something that would snare a security-focused used, but they would most likely never let anybody be scanning their system in the first place.

MD5s can possibly be reverse engineered or cracked, but the chances of two files in the wild accidentally having the same MD5 are beyond astronomical. MD5's are perfectly acceptable for doing file comparisons. Besides MD5s were just being used as an example. They may be using SHA or something else.