"As of August 31st, we will no longer be able to support the retrieval of license keys for the songs you purchased from MSN Music or the authorization of additional computers," Microsoft said in an e-mail that was sent Tuesday to former MSN Music customers.
That means consumers who purchased songs from MSN Music and who want to port their library to a new device -- in case of, say, a hardware failure or desire to upgrade -- won't be able to do so after the end of August.
Given the life of today's computer hardware and mobile devices, Microsoft's decision effectively places an expiration date of about three to five years on song libraries that MSN Music customers thought they had purchased for life.
Microsoft did not provide a reason for the decision.
Microsoft launched MSN Music in 2004 in an effort to counter Apple's successful iTunes brand. But the effort failed to take off, and Microsoft killed MSN Music in 2006 after it launched an MP3 music player of its own called Zune.
Zune users can now download their tracks from Microsoft's authorized Zune Store.
Microsoft is among the many digital entertainment vendors that employ DRM technologies to ensure that content is not stolen. The technology sends a message from the user's playback device to a central server, which verifies a license key embedded in music and video files.
If the license key is not confirmed, the file won't play.
Critics of DRM, including the Free Software Foundation, argue that users who purchase digital content outright should not have any restrictions placed on how they can use their downloads.