The hacker-activist group Anonymous says it’s holding important government files hostage to avenge the death of Reddit co-founder Aaron Swartz.

The techies, who blame the feds for Swartz’s suicide, hijacked a Department of Justice Web site yesterday, saying they’ll release agency secrets if the United States fails to reform its justice system.

The group took control of the Sentencing Commission’s site, posting a video on the home page, claiming “a line was crossed” by the Internet hero’s prosecution.

The virtual hijack comes after friends, family and online activists claimed Swartz killed himself because he was being unfairly prosecuted for allegedly breaking into the Massachusetts Institute of Technology.

Swartz, who also helped create the RSS feed, hung himself at his Brooklyn apartment Jan. 11.