There have been numerous Monopoly video games based on the core game mechanics of Parker Brothers and Hasbro's board game Monopoly. They have been developed by numerous teams and released on multiple platforms over 35+ years. Many unlicensed non-commercial computer games based on Monopoly were distributed on bulletin board systems public domain software disks and academic computer systems and appeared as early as the late 1970s. At the time Parker Brothers was unaware of this distribution until a user informed them of one version that stated "A Parker Brother game" on the title screen; the company then began enforcing its copyright and trademark on Monopoly.