Copyright on vintage software is a a gray area. The Library of Congress issued an exemption to the DMCA in regards to vintage software. You're allowed to crate an archive of abandonware, including ways to circumvent copy protection. However, the definition of what constitutes as an "archive" and "abandonware" is rather dubious.

Wikipedia has a good section on the legality of distributing vintage software. Basically, the exemption to the DMCA that enables copying and archiving vintage software is untested. Fortunately, there are no companies (as far as I know) that have filed any DMCA takedown notices for any of the popular abandonware sights (Underdogs, Abandonia, etc.)