Copyright gives the author of an original work exclusive right for a certain time period in relation to that work, including its publication, distribution and adaptation, after which time the work is said to enter the public domain. Copyright applies to any expressible form of an idea or information that is substantive and discrete and fixed in a medium. Some jurisdictions also recognize "moral rights" of the creator of a work, such as the right to be credited for the work. Copyright is described under the umbrella term intellectual property along with patents and trademarks.
The term sharing is not illegal, but your authority to do so and the effects of it may lead to being illegal.
If your county/place has LAWS governing the intellectual property rights of the original authors, then that's illegal.
however, tracking a single user can be tough(talk about millions) that's y they only/usually catch those who download for free and sell them without proper authorization from the original authors...