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Copying of information goods which are downloaded (rather than being mass-duplicated as with physical media) can be inexpensively customized for each download, and thus restricted more effectively, in a process known as "[[traitor tracing]]". They can be encrypted in a fashion which is unique for each user's computer, and the decryption system can be made [[tamper resistance|tamper-resistant]].
Copy protection for early home computer software, especially for games, started a long cat-and-mouse struggle between publishers and [[software cracking|crackers]]. These were (and are) programmers who would defeat copy protection on software as a hobby, add their [[pseudonym|alias]] to the title screen, and then distribute the "cracked" product to the network of [[warez]] [[Bulletin board system|BBSes]] or [[Internet]] sites that specialized in distributing unauthorized copies of software.
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There is also the tool of [[software blacklist]]ing that is used to enhance certain copy protection schemes.
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During the 1980s and 1990s, video games sold on [[audio cassette]] and [[floppy disk]]s were sometimes protected with a user-interactive method that demanded the user to have the original package or a part of it, usually the manual. Copy protection was activated not at installation but every time the game was executed.<ref>[[Retro Gamer]] issue 83, "Don't copy that floppy"</ref>
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While not strictly a software protection, some game companies offered "value-added" goodies with the package, like funny manuals, posters, comics, storybooks or fictional documentation concerning the game (e.g. the Grail Diary for Indiana Jones or a police cadet notebook with ''[[Police Quest]]'' or the Hero's manual of ''[[Quest for Glory]]'' or a copy of the ''National Inquisitor'' newspaper in ''[[Zak McKracken]]'') in order to entice gamers to buy the package. This trend is re-emerging in modern gaming as an incentive to both buy games and discourage their resale; some games like ''[[Forza Motorsport 3]]'' and ''[[Dragon Age: Origins]]'' provide bonus in-game material that will only be given if one buys the game new.
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When Sega's [[Dreamcast]] was released in 1998, it came with a newer disc format, called the [[GD-ROM]]. Using a modified CD player, one could access the game functionality. Using a special swap method could allow reading a GD-ROM game through a CD-ROM just using common MIL-CD (standard CD Boot loading, commonly found on Windows Installation Discs, Linux Live CDs, and others). Dreamcasts sold after October 2000 contain a newer firmware update, not allowing MIL-CD boot.
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The [[PlayStation 3]] uses Blu-ray [[Blu-ray Disc|BD-ROM]] discs. In addition to any protection provided by the console itself, the BD-ROM format's specification allows for a [[ROM-Mark]] which cannot be duplicated by consumer-level recorders. The BD-ROM format, in addition, has a notably large file size in the neighborhood of 40-50 gigabytes per game, making it unwieldy for online file-sharing, a major method of video game copying.
Companies such as [[Macrovision]] and [[Dwight Cavendish]] provided schemes to [[videotape]] publishers making copies unusable if they were created with a normal [[VCR]]. All major videotape duplicators licensed Macrovision or similar technologies to copy protect video cassettes for their clients or themselves.
Starting in 1985 with the video release of "[[The Cotton Club (film)|The Cotton Club]]", Macrovision has licensed to publishers a technology that exploits the [[automatic gain control]] feature of VCRs by adding pulses to the vertical blanking sync signal.<ref name="copy_prevention_patents">Some relevant patents are {{US patent|4631603}}; {{US patent|4577216}}; {{US patent|4819098}}; and {{US patent|4907093}}.</ref> These pulses do not affect the image a consumer sees on his TV, but do confuse the recording-level circuitry of consumer VCRs. This technology, which is aided by U.S. legislation mandating the presence of automatic gain-control circuitry in VCRs, is said to "plug the analog hole" and make VCR-to-VCR copies impossible, although an inexpensive circuit is widely available that will defeat the protection by removing the pulses. Macrovision has patented methods of defeating copy prevention,<ref name="copy_prevention_defeat_patents">One such patent is {{US patent|5625691}}.</ref> giving it a more straightforward basis to shut down manufacture of any device that descrambles it than often exists in the DRM world.
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By 2000, [[Napster]] had
CD copy protection is achieved by assuming certain feature levels in the drives
The play preventions in use intentionally deviate from the standards and intentionally include malformed multisession data or similar with the purpose of confusing the CD-ROM drives to prevent correct function. Simple dedicated audio CD players would not be affected by the malformed data since these are for features they do not support — for example, an audio player will not even look for a second session containing the copy protection data.
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Examples of CD copy protection schemes are [[Cactus Data Shield]], [[Copy Control]], and [[Data Position Measurement]].
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More recently, publishers of music and films in digital form have turned to [[encryption]] to make copying more difficult. [[Content-scrambling system|CSS]], which is used on DVDs, is a famous example of this. It is a form of copy protection that uses [[40-bit encryption]]. Copies will not be playable since they will be missing the key, which is not writable on DVD-R or DVD-RW discs. With this technique, the work is encrypted using a key only included in the [[firmware]] of "authorized" players, which allow only "legitimate" uses of the work (usually restricted forms of playback, but no conversion or modification). The controversial [[Digital Millennium Copyright Act]] provides a legal protection for this in the US, that would make it illegal to distribute "unauthorized" players—which was supposed to eliminate the possibility of building a DVD copier. However, encryption schemes designed for mass-market standardized media such as DVD suffer from the fundamental weaknesses that consumers have physical access to the devices containing the keys, and once implemented, the copy-protection scheme can never be changed without breaking the [[forward compatibility]] of older devices (or the [[backward compatibility]] of newer media). Since consumers are highly unlikely to buy new hardware for the sole purpose of preserving copy protection, manufacturers have been prevented from enhancing their DRM technology until recently, with the release of next-generation media such as [[HD DVD]] and [[Blu-ray Disc]]. This period represents more than enough time for the encryption scheme to be defeated by determined attackers. For example, the CSS encryption system used on DVD Video was broken within three years of its market release in November 1996 (see [[DeCSS]]), but has not been changed since, because doing so would immediately render all DVD players sold ''prior'' to the change incapable of reading new DVDs—this would not only provoke a backlash amongst consumers, but also restrict the market that the new DVDs could be sold to. More recent DVDs have attempted to augment CSS with additional protection schemes. Most modern schemes like [[ARccOS Protection]] use tricks of the DVD format in an attempt to defeat copying programs, limiting the possible avenues of protection—and making it easier for hackers to learn the innards of the scheme and find ways around it.
The newest generations of optical disc media, [[HD DVD]] and [[Blu-ray Disc]], attempt to address this issue. Both formats employ the [[Advanced Access Content System]], which provides for several hundred different decryption keys (for the varying models of players to hit the market), each of which can be invalidated ("revoked") should one of the keys be compromised. Revoked keys simply will not appear on future discs, rendering the compromised players useless for future titles unless they are updated to fix the issue. For this reason, all HD-DVD players and some Blu-ray players include an [[Ethernet physical layer|ethernet]] port, to give them the ability to download DRM updates. Blu-ray Disc goes one step further with a separate technique called [[BD+]], a virtual machine that can execute code included on discs to verify, authorize, revoke, and update players as the need arises. Since the protection program is on the disc rather than the player, this allows for updating protection programs within BD's working life by simply having newer programs included on newer discs.
== Notable
Over time, software publishers (especially in the case of video games) became creative about crippling the software in case it was illegally copied. These games would initially show that the copy was successful, but eventually render themselves unplayable via subtle methods.
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* On a copied version of the original PC version of ''Postal'', as soon as the game was started the player character would immediately shoot himself in the head.
* The pirated version of [[Serious Sam 3: BFE]] spawns in a large immortal monster early on in the game.<ref>http://www.rockpapershotgun.com/2011/12/07/serious-sams-drm-is-a-giant-pink-scorpion/</ref>
* A pirated copy of Pokémon Black or White runs as it was normal, but the Pokémon
* If [[Gyakuten Kenji 2]] detects a pirated or downloaded copy of the game, it will convert the entire game's text into the game's symbol based foreign language, Borginian, which cannot be translated in any way.
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{{too many see alsos|date=November 2011}}
* [[Alcohol 120%]]
* [[Aladdin Knowledge Systems]]
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* [[Vendor lock-in]]
* [[Watermark detection]]
== Notes and references ==
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