DMCA outlaws tools that allow circumventing copy-protection technologies, such as CSS. Previously studios have attacked against distributors of freeware tool DeCSS and against the 321 Studios, the creators of DVDXCopy.
Most of the companies now sued are simply selling DVD backup products via their websites and according to various sources, some of them simply sell packages made out of freeware tools. At least one of the companies in question, QOJ, has managed to get itself into virtually all known spam blacklists in the world with their domain copiesanything.com. Tritton is the only one of the companies now sued that has brick-and-mortar distribution deals with major retailers in the U.S.
More information:
BusinessWeek
Wired