This article is from the Anime Music FAQ, by Ru Igarashi with numerous contributions by others.
In all Berne convention signatory nations, yes, they are. These are made by Taiwanese companies that did not get permission, or pay licenses, to reproduce and distribute most (if not all) of their anime CDs. As far as the CD data for a given song is concerned they are identical to the original. They are also getting difficult to identify by package quality, as their print copying is getting pretty good.
Other common bootleg companies seem to be: Smile Face Alion
It is up to the you to decide if buying a bootleg is acceptable to you. Similarly, it is up to you how you should react to a store that sells bootlegs.
Note: As of 1 January, 2002, Taiwan joined the World Trade Organization, and thus became obliged to enforce international copyright. The current batch of bootleggers (Son May, Ever Anime, Smile Face, Alion) are expected to disappear soon.
 
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