WASHINGTON — The Justice Dept. announced Thursday that its antipiracy effort, code-named “Operation Counter Copy,” resulted in 35 indictments for alleged infringement last April.Among the indictments were five against video pirates and three against sound recording pirates. Both the Motion Picture Assn. of America and the Recording Industry Assn. of America praised the Justice Dept. effort to combat the $20 billion-a-year counterfeit business. Operation Counter Copy is a joint effort by the Justice Dept., the Federal Bureau of Investigation and the U.S. Customs Service. “For too long, pirates in this nation have operated in a low-risk, high-reward environment,” said MPAA president Jack Valenti. The RIAA’s Hillary Rosen singled out the federal investigators who worked on the case. “The resolve and contributions of these men and women, and the agencies they represent, have enabled the RIAA’s antipiracy unit to make significant strides in fighting domestic music piracy,” said Rosen.