The Red Book CD-DA audio specification does not include any copy protection mechanism other than a simple anti-copy flag. Starting in early 2002, attempts were made by record companies to market "copy-protected" non-standard compact discs. Philips stated that such discs were not permitted to bear the trademarked "Compact Disc Digital Audio" logo because they violate the Red Book specification. There was great public outcry over copy-protected discs because many saw it as a threat to fair use. For example, audio tracks on such media cannot be easily added to a personal music collection on a computer's hard disk or a portable (non-CD) music player. Also, many ordinary CD audio players (e.g. in car radios) had problems playing copy-protected media, mostly because they used hardware and firmware components also used in CD-ROM drives. The reason for this reuse is cost efficiency; the components meet the Red Book standard, so no valid reason existed not to use them. Other car stereos that supported CD-ROM discs containing compressed audio files (such as MP3, FLAC, or Windows Media) had to use some CD-ROM drive hardware (meeting the Yellow Book CD-ROM standard) in order to be capable of reading those discs.