RipGuard is a copy protection mechanism developed by Macrovision. Since Content Scrambling System (CSS) on retail DVDs is so easy to circumvent using free widespread software, several methods to discourage making proper copies of DVD-Video content have been devised and put out on the market.
RipGuard's sole reason for existence is to disrupt software made for DVD ripping purposes. When RipGuard was first announced by Macrovision, the company tried to market it using a claim that it could defeat 97% of all DVD ripping software available. At the same time, Macrovision was also using its legal arm to target ripping software that could easily circumvent its technologies.
As an example, Macrovision went after the author of the popular DVD Decrypter utility and subsequently acquired the rights to the software. The company then sent warning letters to sites hosting the DVD Decrypter tool demanding it be removed while threatening further legal action if it remained on offer.
Despite Macrovision's claims about RipGuard, and any efforts to stomp out ripping utilities online, RipGuard can reportedly be beaten easily using either commercial software like Slysoft's AnyDVD, or freeware like DVDFab Decrypter. RipGuard is also controversial in that there are confirmed cases of its inclusion on DVD media resulting in content playback problems.