Software cracking (known as "breaking" mostly in the 1980s) is the modification of software to remove or disable features which are considered undesirable by the person cracking the software (software cracker), especially copy protection features (including protection against the manipulation of software, serial number, hardware key, date checks and disc check) or software annoyances like nag screens and adware. A crack refers to the means of achieving, for example a stolen serial number or a tool that performs that act of cracking. Some of these tools are called keygen, patch, loader, or no-disc crack. A keygen is a handmade product serial number generator that often offers the ability to generate working serial numbers in your own name. A patch is a small computer program that modifies the machine code of another program. This has the advantage for a cracker to not include a large executable in a release when only a few bytes are changed. A loader modifies the startup flow of a program and does not remove the protection but circumvents it. A well-known example of a loader is a trainer used to cheat in games. Fairlight pointed out in one of their .nfo files that these type of cracks are not allowed for warez scene game releases. A nukewar has shown that the protection may not kick in at any point for it to be a valid crack. Software cracking is closely related to reverse engineering because the process of attacking a copy protection technology, is similar to the process of reverse engineering. The distribution of cracked copies is illegal in most countries. There have been lawsuits over cracking software. It might be legal to use cracked software in certain circumstances. Educational resources for reverse engineering and software cracking are, however, legal and available in the form of Crackme programs. History The first software copy protection was applied to software for the Apple II, Atari 8-bit family, and Commodore 64 computers.. Software publishers have implemented increasingly complex methods in an effort to stop unauthorized copying of software. On the Apple II, the operating system directly controls the step motor that moves the floppy drive head, and also directly interprets the raw data, called nibbles, read from each track to identify the data sectors. This allowed complex disk-based software copy protection, by storing data on half tracks (0, 1, 2.5, 3.5, 5, 6...), quarter tracks (0, 1, 2.25, 3.75,