Video games are a multi-billion dollar industry. In 2014, games generated $22 billion in revenue according to the Entertainment Software Association (ESA) [source: ESA]. Software is digital in nature, making it easy to save and distribute online, but like books, movies, songs and other artistic works that can be copied and distributed, software code is subject to copyright laws. Pirating software that's available commercially is clearly illegal and risky, but in the case of abandonware, the ethics and risks become more questionable in a lot of people's eyes, even if the legalities are fairly straightforward.
Technically, any intellectual property that's still under copyright can only legally be reproduced and distributed by the owner, or by anyone granted distribution rights by the owner via a license or other legal agreement. Some aspects of the software, like the name or logo, might also be protected by a trademark.
Copyright lasts a long time, longer than most software has been around. Ever since the Sonny Bono Copyright Term Extension Act of 1998, U.S. copyright for most works (created on or after Jan. 1, 1978) lasts 70 years beyond the life of the author, or, in the case of works created by companies or as works-for-hire, 95 years from publication or 120 years from creation (whichever expires first). Civil penalties for infringement can carry anywhere from a $200 to $150,000 fine per work, or the actual monetary loss to the owner. Possible criminal charges can result in up to five years imprisonment and $250,000 in fines, although a smaller settlement or a cease-and-desist letter have been more common [sources: BSA, Cornell, U.S. Copyright Office].
Even though the time from a software application's release to its relative obsolescence is just a few years, home computer software has only been around for a few decades, so it's essentially all still under copyright, unless the copyright holder has voluntarily put it into the public domain. That means most abandonware is still copyrighted, and a lot of software companies consider it infringement to download and use it.
Both distributing and downloading copyrighted works without permission is considered infringement, so technically if you're getting software from some route other than an authorized source, the owner could come after you or the download site for infringement. It can even be considered infringement if you download a game you have already purchased and still own in another form. Although the Library of Congress did make an exemption to the 1998 Digital Millennium Copyright Act in 2006 to allow users to hack the copy protection on software for computers that are no longer sold or supported for archival purposes, as well as games with copy protection that required physical dongles that could no longer be replaced [sources: Beschizza, Boyes].
Software companies sometimes see old games as competition to their on-the-market games [source: Costikyan]. And companies that don't protect their intellectual property rights when they know infringement is going on actually risk losing some of their rights [sources: Francis, Moby Games]. Industry groups such as the ESA (formerly the Interactive Digital Software Association), and the Software and Information Industry Association (SIIA) try to fight piracy and other copyright infringement of the works of their members. In 1997, when abandonware sites were just starting to come into being (and when the term was coined), these organizations sent cease-and-desist letters to the sites, leading most of them to shut down [sources: Granade, Huthwaite]. However, more abandonware sites sprang up in their place and some of the old sites were resurrected.